Crossed stays on the best
I do what Brenna Noble does.
I have shorter are leg straps, so I crops them. My mare has never got her legs caught while rolling.
I attach the first one to the same side, then with the second, stick it through the first before clipping it to its respective side. This prevents them from sliding down the leg at all while still not being too tight. I've never had a horse get caught or seem uncomfortable with them like this and I find it works best to keep the blanket from sliding side to side.
I don't cross the leg ones, if you cross them the horses legs can get stuck. But I do cross the under the belly ones because if they aren't crossed there's a slight possibility that the legs could get stuck
I prefer to not cross the as thats how a horse can get their leg stuck while rolling but if you dont cross them they dont get stuck