iopq's answer was correct, but I'm going to prove a more general case with some algebra.

Suppose we go all-in for s into a pot of 1 with x equity against 1 opponent who has us covered. Our EV when our opponent folds is 1, and our EV when our opponent calls is:



So when would we be rooting for a call? When the EV of a call is greater than the EV of a fold, or:



We can play with this equation a bit by isolating our opponent's equity (1-x):

[MATH OH NOES]

[/MATH OH NOES]

When we bet all-in for s into 1, our opponent is calling s in a pot of s+1, so the equity he needs to break even is s/(2s+1). Since 1-x is our opponent's equity, we have shown that we are rooting for a call when our opponent's equity is less than s/(2s+1).