I bought a used, older Specialized Allez. Based on how the bike was set up when I got it, it’s clear the previous owner wasn’t much into minor adjustments. So, I’m slowly trying to get the bike dialed in to my personal liking, which includes the handlebars. FWIW, they are the Ritchey 6016 T-6 Alloy drop bars. They have ergonomic drops similar to the one pictured below. And among all my bikes, this is actually the first one I’ve owned with ergonomic drops. Understanding that final adjustments are based more on my personal liking rather than aesthetics. My question is this: That small flat part at the lower end of the drops that I’ve indicated with the arrows…for ergonomic alignment, is that short flat supposed to be level? — Dan

The common thinking (FWIW) is that the drop portion could be level or pointing toward the rear axle - or anything in between. A lot depends upon where you mount the brifters.

This example is a bit extreme as the drop portion points below the rear axle.

Agreed. Indeed, almost all of how you align your drops is drive by where you mount the brake levers. I always align the tip of the lever with a straight edge along the flat part of the drops. On modern bars that aligns the ramp of the lever with the ramp on the bar. Then, I set the bar angle so the flat of the drops is between level and point at the rear brake bridge.

EDIT: On the example above, I'd say the levers are set too low, requiring the bar to be angled higher for comfort. See below.

If you like it flat or level with the ground, then you can do that. But I and others rotate the bar so that the STI's provide us a comfortable transition where they meet the bar. And that tends to be when pointed toward the rear axles as the pictures above show. But if your aesthetics outweigh the other things for you, then do what you wish.

There are two principles at play here: fit and aesthetics. For pleasing aestheitcs, handlebars must be rotated to adhere to the "rule" (which changes over time and local peer review). For many, this means the straight portion of the lower drop must be horizontal. Or pointed at the rear brake mounting bolt. Or some point in between. Or the slope into the forward rounding (above and behind the brake levers) must be level or some other chosen angle. (Modern bars often have so little straight at the lower drop ends that the concept of "horizontal" is approaching meaningless.)

Then there is fit. Some of us are passionate about the rotation of the handlebars being perfect for comfort; allowing for all day rides and hard efforts, even maximum efforts, without injury, pain or chronic issues. I"m in that category. The end result almost always ends up between the brake bolt and horizontal. I often mark that place with a piece of tape, but only so I can pull the bars off and replace exactly where they were or have a reference so I can do mid ride adjustments to rotation and not loose my starting point.

An aspect of the fit - some of us age and acquire injuries, chronic issues, etc. from time spent in sports, the military, industry, with power tools, riding bikes .... and have issues that mean handlebars that adhere to the rules physically don't do well for us or perhaps not work at all. If "perfect" bike setup is really important, I recommend staying away from such activities (including riding bicycles).

I’ve also noticed that the diagonal part of the drop, just above that small flat at the end…what I would think is where your hand would grasp…currently isn’t in an ergonomic angle position for me. I.e. when I grasp onto that diagonal my wrist is ‘cocked’ a bit. And, over a long period on the drops it seems that would be irritating. If/when I do adjust the bar so that the small flat at the end is level, it would make the diagonal just about perfectly ergonomic for me. But of course, there’s a chain of adjustments required if/when I do adjust the handlebars. The brifters will need to be moved, and then the cables/housings length will likely need to be altered, and adjustments at the brake calipers, and derailleurs. — Dan

I tried some ergonomic bars once. They weren't for me. I didn't find them comfortable either. But perhaps the slight differences between some brands makes a difference. And maybe it's much like saddles. Everyone prefers something different.

I just like the short reach shallow drop bars. Ergonomics doesn't seem to be needed for me.

I started road cycling in the 11-speed era, so my only experience is with ergonomic drops. No super deep U-shaped handlebar for me!

For both aesthetic and ergonomic purposes, I align the ends of the drops so they are just about parallel with the longitudinal axis of the slanted top tube. This puts the ramps of the handlebar at the perfect angle for how I mount my Shimano STI levers.

Above underlined terms used with reference to Bike Gremlin's drop bar section names: Drop bar hand positions (Hoods, Drops etc.) | Bike Gremlin US.

in general...yes...flat or parallel to the ground...but personal preferences for comfort, etc. take precedence...

Comfort & Fit are certainly important. One additional attribute that should be mentioned is Safety. In the photo provided (with the Campy levers) - the drops are borderline too jacked up to assure downhilling that is properly planted. I prefer a generous section of the drops to be horizontally parallel to the ground. This position can also be more aero for descending. If my back doesn’t like longer road segments in the drops I can utilize the tops of the bars more and reserve the drops mostly for swift, safe descending. But in the past few years I seem to have discovered a trick of front rotated pelvic positioning on the saddle that seems to allow a flat back and the hands drape naturally down to the drops where you can hang out for longer percentages of your ordinary riding terrain than you might think.