Yes that's my point. You're saying there's greater thump if there's greater reserve. If that's true, selecting a higher gain (which has more reserve) woukd produce more thump at same volume.
Not true at all. Only true if the lower gain isn't enough to allow for dynamic peaks (reserve).
Say the LCD-2.2. At 110dB, which is enough reserve for dynamic peaks, you need 2Vrms and 80mW. That has enough reserve. If you have an amp with these power, it will maximize all the thump the recording intended. If you select a higher gain using SAME amp, it won't result to more thump, in fact it will result, if at all, to more treble, at least to my ears.
If you have an amp with gain that doesn't produce power requirements of the HP, then you shift to higher gain on that same amp, that's the time it will produce more thump.
So what you're hearing is a characteristic of the amp's design to have more thump as a whole and in all cases, not because of the more reserve it has. More reserve over and above your listening levels is just that, a reserve that wouldn't be used at all in any case.