All else equal (which they rarely are) soft will give more squirt for two specific scientific reasons.
1. Longer contact time which means more shaft mass in play during contact (based on transverse wave propagation rate down the shaft)
2. Longer contact time for the tip to rotate around the cueball such that the average tip offset is greater than the equal hard tip shot resulting in more squirt.
There is at least one more theory and observation, but I'll leave that to recent tests from Barioni Cues who have been exhaustively working with a cue testing robot (Dyno) of his own design.
Based solely on geometry, with the same centerline aim, a nickel would hit slightly less offset than a dime which would suggest less squirt but less spin.
I struggle with this because there are too many reports that suggest a dime has less squirt. I wonder if the simple act of shaping to a dime significant decreases tip mass. "All things being equal" often aren't.
People aren't answering because its talked to death. The science debates ceased being interesting a long time ago.
If I were you, I'd go to Dr Dave's site
here
I think these particular attributes contribute a small amount to squirt. Latest testings suggest their contribution to squirt as significant or at least more significant than previously considered .
Freddie <~~~ you sure you wanted a science answer?