2.5 Way for a centre speaker?

[Puggie]

I'm looking at building a centre to go with my floorstanders (Morel units), Ideally I wanted a MTM on its side for the centre, and to have it match the stereo pair as close as possible for obvious reasons. But, my stereo pair are using 1st order Xovers and a MTM with 6dB slopes is not likely to work once you are out of the sweet spot, I would have thought 18-24dB slopes would have been needed, but this does change the voicing of the speaker somewhat. My thought was to run a 2.5way using one midbass crossed with the tweet and the other low passed to compenate for the baffle step. Now how to I go about this without causing phase problems between the two midbasses from the roll off of the bass (.5) going out of phase with the midbass.

Any thoughts on this? how should I filter the bass (.5) speaker to avoid any cancellation with the midbass. or should I consider going 3 way using one driver for the mid and crossover to the other for the bass, I can get both 4 and 8 ohm drivers so I could use the lower impedance driver to compensate for the baffle step response.