The bleed circuits are like a straw with a hole in the side so the bottom of the straw is submerged in fuel , the hole in the side is the jet or idle screw restriction & the top of the straw is the bleed , so the vacuum in the venturi or manifold draws in fuel through the jet or idle circuit , if you close the top of the straw vacuum will pull 100% through the idle or jet , the larger the hole at the top of the straw the less effect the vacuum has on fuel flow through the jet or idle circuit .
So with higher engine vacuum either in the manifold or venturi you need a larger bleed to lessen the pull / fuel flow & with lower vacuum you need a smaller bleed to increase fuel flow .
I hope this helps