I suspect a radius or chamfer will work equally well. My understanding is that removing the 90° corner at the inside edge of mid/woofer driver opening to reduce diffraction is the key element. There is also another element that may come into play with thicker baffles. Without flaring the woofer cutout some way, the effect is that of forcing the back wave of driver into a "tunnel" of sorts. Not a huge concern with 3/4" material.
Danny has recommended a minimum of 3/8" radius on the backside of woofer opening, I imagine the same would hold true of a chamfer. I've seen that taken to extremes, but at some point one starts to interfere with the driver mounting holes, which opens yet another can of worms that has been debated ad nauseum.
Cut it at 3/8 or 1/2" and know you've done what's necessary. It seems to me splitting theoretical hairs is just fuel for forum debates and has little audible effect on sound of a given design.
