LSX has a galvo resonance safety feature built into it that ensures a minimum number of points are displayed. This minimum number varies by DAC and by projection speed. The difference between your frame (plus any added points defined in your optimization settings) and this 'minimum number of points' are blank points, thus you not getting a higher modulation value to your driver.
I don't know what DAC you are using, but you can do an ILDA export to see exactly how many total points there are and how many blank points were added. As general guidance though, the Etherdream DAC requires 100 total points per 10KPPS - so you need 400 points minimum (again after added points defined by your optimization settings) for 40KPPS. You still won't get to a modulation of 5.0V no matter what you do, but you should be able to something akin to 4.8V.
-David
"Help, help, I'm being repressed!"