The bag has two connection points a lower (for use without extensions) and a higher (for use with the extensions). When the extensions are not in use, the top few inches of the bag become effectively an extension collar. Compression and everything else moves down accordingly. The Drawstring bag is optimized for the higher frame height (so the drawstring is higher than the end of the frame) but it will work fine at the lower height. The Roll Top bag, the closure height really doesn't matter. Both pack bags have a bit of play and adjustment within a couple inches, so if you actually wanted to trim your frame to a certain height within an inch or two you certainly could.
To note, I find a 26" frame is fine for me up to 130 lbs and I am 6'1". I can use a packbag at it's standard attachment on the 26" frame due to the play in the attachment. For me, 24" is about the minimum to get any lift at lower load limits perhaps to 40 or 50 lbs. I could go with a 24" with extension and it will work perfectly fine, however the 26 is a nice mix for me. The hipbelt works very well, even when it is not centered perfectly on the illiacs, so I can just increase torso of the the harness and drop the belt a couple inches if I need to and function fine at lower weights. For me either are acceptable. I'd prefer frame extensions and being perfectly centering on the iliacs for busting brush, but I hunt a lot more open country and can be fine with 26. The extensions work great, and this is just a demonstration of the flexibility. If I feel 26" is to long, I'll cut it to 24 and use the extension for the heavier loads.
