All the bombers in AH fly faster than they did historically, due to the games engine management, so letting them go up to 28k is no good for a design.
The map is also not to scale, so a bomber formation can "burn along" at 100 power, and really have no issues with fuel to rtb with, not so on a 1:1 scale map of Europe.
23k is a very reasonable alt cap, its also historically accurate. Bombing at 28k was not done by the 8th AF, as the accuracy it was looking for could not be achieved at those heights.
Any alt cap above 19k is fine for this kind of setup, imho. Thats plenty of alt.
There are tried and true reasons why the CMs set alt caps. FSOs have special rules, and they are there for a purpose.