I am finally getting around to installing the 6700 shifters but due to the different shape and size of them compared to my 5600 shifters, I'm having difficulty deciding where (in relation to the handlebar) I should attach them.

Is there an easy guideline to installing shifters on the handlebars? It looks like the hoods of my 5600 shifters are installed so that top of the hoods are inline with the top of the handlebar (just before it starts curving down I mean). Is this a good starting point or is there any other method to determine the shifter location on the handlebar?

Thanks in advance,

it depends on your bars.

But usually the ends of the bar should sit flat with the tips of the brakes.
alternatively, the top flat section should be flat with the hoods.

good modern bars allow both.

Thanks,

I have my current 5600 shifters flat with the top of the bar right now. I'll install the 6700 shifters to be flat at the top as well.

The location of the end of the brake lever is coincidental and has nothing to do with proper placement of the brake hood. You want the area where the palm rests to either be horizontal, or angled upward just a few degrees.

Always adjust the bars first, so the hook portion is angled as desired, for comfort when the hands are in the hooks, then position the brake hood. This is most important with "anatomic" bends that do not have the traditional round-bend in the hook area.

I've used a lot of different bars in the last 10 years and always had the end of the brake lever far above the bottom of the bars. Most recently, I've used the Easton EC90-SLX3 short reach bars.

I would disagree, because that's how every major maker tells you to align the brake levers for drop bars. The hoods should be aligned to parallel with the ground or slightly raised OR the ends of the bars should be slightly raised from parallel to the ground. If the hoods don't line up with the tops of the bars, then that's just the bars. If the bars give a poor position for the levers, then it's just the bars.

The important part is choosing some bars that allows proper lever placement while being comfortable to the rider.

If you find yourself needing the bars in an improper position, then it's most likely something wrong with your fit.
Exceptions are only if a rider has reduced functionality of their arm(s) or the bars are special, like dirt drops.

I say pick a start point that follows the "flat with the top of the bar" advice. Ride around a bit before taping the bars...looks kind of funny, but you can tweak the position and play with changes. If you hate it, nothing lost and you can adjust.