I'm confused then. I have eliminated my understeer by keeping my front tires at the maximum door jamb pressure (32) and the rears in the towards the low/middle side of pressure.
I don't have understeer...mine it pretty neutral right now. When I apply gas lightly through turns, I push out the rear end and definitely notice throttle steering.
You might increase the throttle steering response with higher pressure, but a little more pressure does make the tire diameter greater, and thus the same angle of steering causes more turning.
This is what I've read in many places and have direct experience with...just saying.
Mango, I agree, though, that I bet a lot of time has to do with contact patch and that using door jamb, even at autoX might be better than 40 all around (though that might be closer to your recommended pressures than mine). I'm 29-32 in front and 33-41 in rear (I think).