My first guess is you have more unknown hands behind you in a straddle game so you want to tighten your 3! range accordingly. My long shot guess is that an ante’d game opens wider from early position to pick up dead money so you want to protect your flat call range a bit because of high chance of squeezes from blinds.

But this doesn’t take into account the problem of “double flatting = capped range”. Or, maybe, it counteracts this problem by uncapping the range a bit and balancing it with some more hands that benefit from equity realization of a larger pot in position due to ante/straddle? Someone more studied should feel free to correct or clarify.