Links to info about proper crossover design wrt phase

Hi any good links to some information on how to optimize two way crossovers for ideal phase response at the between the woofer and tweeter? I've searched but I'm suffering from information overload so I'm hoping for a few links (or references to books) to get me started. I'm using active crossovers if that matters.
 
Are you trying to control phase to be where you want it, or are you trying to calculate power through the cross?

To answer the first question as it is the more often asked, phase goes along with the slope. For example, if you manage two fourth order acoustic slopes, their phase should just line up, notwithstanding delays and other things.
 
Thanks. So when the measured acoustic slopes match it's essentially a non-issue then? How much leeway is there are we talking perfect match or maybe a few dB difference are okay to still have what's considered sorted-out phase between the driver's?