Originally Posted by
Brian Holcombe
Tom is accurate in my estimation, technically you need a lapping plate larger than the sole of the plane. That’s a big plate for a #8.
A plane sole doesn’t need to be perfectly flat but a hump behind the mouth will certainly cause issue. Certain shapes are no problem, and certain shapes are a problem.
Twist would be a problem, a hump behind the mouth would be a problem. A smooth curve with the mouth being the highest point (point contacting the wood) should not be a problem unless it's curved a lot. A curve where the ends are the highest point may present a problem unless the plane flattens out from its own weight.