I had my bike on the stand, adjusting my SRAM Force rear derailleur, and was having trouble getting it to drop down onto the smallest (outer) cog, even after adjusting cable tension for proper shifting across the range of cogs all the way to the large (inner) cog.

Seems like the high (H) set screw must need adjustment. I'm pretty sure that adjustment would be to turn the H set screw counter-clockwise, to move the set screw out. However, at that point I realized the set screw was already out pretty far. I tried unscrewing it even further, but that didn't help.

Any other ideas? Is a bent hanger the most logical culprit? If that's not it, what else might it be?

My first thought is the cable is too tight, start by going full in on the barrel adjuster, force the chain to the small cog if needed, loosen the pinch bolt, screw the barrel adjuster out a few clicks, pull the cable lightly taught, tighten the pinch bolt, adjust tension again.

If cable tension reset doesn't work, start from the beginning by removing the chain, and align the jockey wheel. The high adjustment screw on mine looks like it is all the way out, although it has three threads remaining on the other side. You can view from the underside to be sure a thread is showing. With the chain off, if the high limit screw is all the way out, and the jockey is not close to aligned, then you know something else is amiss, and if there is a bent hanger, you will be able see the jockey is off kilter.

What change was made that resulted in the need for readjustment?

Thanks! I will take a closer look when I get home and try that.

I was switching out wheels - moving my powertap from my TT bike, which is retired for the remainder of the year, back to my aluminum road training bike (2010 Cervelo S1, this is the original SRAM group it came with). I took the opportunity of it being on the repair stand to go ahead and check the adjustment.

I will follow up after I try the above. Thx again.

Also, be sure the lock ring is tightened to spec, and the axle is seated correctly in the dropouts.

OK, got it working smoothly. The cassette spacer was the culprit!

I started with re-tensioning it, step-by-step as you suggested. It was a reasonable place to start given the limited info I provided. Once I had the cable re-tensioned, however, I was back where I started. That is, when the cable tension was correct for the large/inner cog, the derailleur wouldn't quite shift all the way back down to the small/outer cog. Vice-versa if I adjusted for the inner cog - it wouldn't quite stay when shifted all the way to the large/inner cog.

Next, I played with the tension screw, just in case. It seemed to get slightly better as I got the pulley closer to the cassette, but it clearly didn't solve the problem.

Then, I thought through the problem a little further and wondered if there was something funky with my cassette. My first hypothesis was maybe the small/outer cog was not seated properly on the splines. I removed the wheel, but the cassette looked fine, cogs evenly spaced.

Finally, I removed the casette with my cassette tool and decided to try removing the spacer. This is a Shimano Powertap hub with 10-speed Ultegra cassette, fairly new. I put the cassette back on without the spacer and checked to ensure there was no play. Re-installed the wheel, re-adjusted the tension with the barrel, and FINALLY got it working again. The confirmation to me was that I was able to re-adjust the H-set screw, and it is no longer sticking way out.

That was the solution - removing the spacer.

Does that sound "normal" - having to remove the spacer from the Ultegra cassette to get a SRAM rear der to shift properly?

As far as I know, the spacer is only needed if the freehub is of a length preventing the lockring from being tightened completely, regardless of derailleur brand. Your experience is new to me. I would have thought the H limit screw could have solved the issue (the commonly supplied Shimano spacer that would fit ahead of the big cog is normally only 1mm in width); was the H limit screw retracted completely?

Yes, I practically unthreaded it until it was REMOVED, in the process of troubleshooting.

Your point about only needing the spacer if you can't otherwise tighten the lockring completely is affirming - that is, after I removed the spacer, I still had no problem tightening the lockring with no play left in the cassette.

On most derailleurs (front & rear), you can see if the limit screws are touching the stop tab, so that will let you know if the limit screw is the problem or not.

I tend to set up the limit screws without the cable attached.
centered under the outer cog in both cases H&L.
just push the mech sideways by hand. [against the return spring]

Then, I hook up the Cable.