Bet sizing in multiway pot

[feelixthegreek]

Let's say I underbet for $35 and get two callers. There'll be $180 in the pot and I'll have $120 behind. Do I shut down if a bad card comes on the river? Is that a benefit to underbetting instead of making a PSB?

The trouble to me is that it seems weak not to bet a stack-committing amount, yet it seems awkward to bet $75 then be stuck pushing (or calling getting anywhere from 4-6 to 1) my last $75 into a likely made draw.

Given my EP, might I have been better off going for a c/r to increase my chances of getting all my money in on the turn? What about overbetting the flop, like $20-25?