Mains bleed fuel into the throat, big mains bleed more counteracting some of the need to fatten the low end.
No 45's because I find them too rich at altitude...and I'm on my way back from freaking Colorado! I did get them to work at home well but the climb up to 4-5000' always revealed that the bottom starts to choke. I want it to work everywhere and return good mileage...even at a loss of some power...though 45's absolutely rock at low elevations... 3rd gear wheelies!
2nt leanest clip btw, not from the pointy end. I find the 3rd bleeds more fuel into the low circuit, complicating getting the bottom to run well. Fat mains multiply that problem. I get good throttle response, no hole at needle opening so I see no reason.