It's an interesting one, 'cos there's an argument that tops are completely fine with going down to 60Hz? So why cross at 100Hz?
I'm definitely no expert here, but if a key purpose is to relieve the tops of their low end lows to focus on non-bass frequencies, then crossing over at 150Hz (because the bass combo can easily handle up to this) would be more beneficial than 100Hz. But, as I say, I'm no expert!