You might be confusing things. The frequency dial on the sub is disabled if you've set the switch to "disable". I'm talking about the frequencies Audyssey set in the receiver. Sorry I wasn't more clear.
The problem is, 150-180 Hz crossover is getting pretty high. That's largely due to the fact the NHTs are minimonitors. Meaning they have very little low frequency capability, so the sub crossover has to be set rather high. This will cause the sub to be more easily localized, as in...
I'm guessing you're referring to the LPF for LFE setting? That's a whole separate setting, and 120Hz is generally correct, with any system. There is no gap, because if your fronts are at 150Hz, that means the sub is automatically set to crossover at 150Hz.
There are multiple things going on...