I'm not an expert, but I've done a few comp calls and would be happy to tell you what worked for me.
The tonechannel is drilled at 7/32", the exhaust is enlarged and belled, and I add 1/8" to 3/16" of flat to my tone board (just in front of the cork notch). None of these changes make it easy to blow or keep it from sticking, but when ya pour the coal to it rings like a bell.
Comp toneboards take a ton of time to get right, so don't get in a hurry. Remember that small changes on the toneboard have large consequences in the sound and operation, so tread lightly!
Best of luck,
Bob