but if there were 6k or higher bases near the HQ many people would be more willing to grab a 109G-14/K-4, 190D-9, Ta152, or even a P47x for interception/interdiction duty instead of the Me163.
If so, they would do it far more for psychological reasons than for a true advantage the 6k base is offering them.
A 109G-14 at 100% fuel takes 11 minutes to reach 30.5k from sea level. Lifting from a 6k base would shorten that time by less than 2 minutes only.
A P-51D at 75% fuel takes 14 minutes to reach the same altitude. A 6k base would reduce that time by only about 2.5 minutes.
Many bases currently close to the HQ are higher then sea level, sometimes reaching 4k and more, so the net effect of a 6k base would be even smaller. The advantage of high altitude bases for high (20k+) altitude sorties is generally very much overrated, for bombers even more than for fighters.
The main problem is that players do not identify HQ/strat raids in time. They have, for whatever reasons, no battle or map SA. If something doesn't make a base flash, it's not of any interest. And the only plane that can hope to catch a raider when the strats/hq are already flashing is the Me 163.