That's a very interesting experiment, sounds fun. Lots of things changed, the crossover and the cabinet, so I think it might be hard to identify which did which. My hunch is that the crossover change probably had the most effect from about 1kHz up. But going from monopole to dipole would change the directivity below that, and it would obviously decrease bass too.The differences in the crossover will modify directivity, and going from monopole to dipole will change directivity too. They're also likely to change the spectral balance, both directly because of their different filter functions and indirectly because the change in directivity and phase causes different interactions between the drivers.