I like to try to build a bit of cake on the bottom. Lawrence does not and so, I guess, is proof that it is not essential.
For a new pipe, it is often recommended that you start with something like a quarter bowl for the first smoke, maybe the first couple. Then half bowls. Then 3/4. A less than full bowl will help with the overheating a bit. Also, remember that it is not essential that you smoke the entire bowl in one sitting. If you puff for a while, and it gets too hot or you have other things to do (how annoying) you can simply set it down and come back to it later. Also, if it is that hot towards the end of the bowl you are probably puffing too quickly and need to slow down a bit.
You should never feel like you need to puff away like a madman in order to simply finish the bowl. You can always come back to it after it has cooled down.
I'm quite sure that if you could measure the cake thickness in one of my bowls it would be uneven. It is probably thickest around mid bowl and probably thinnest in the heel. I'm also guessing that this is pretty common. There are, like, 6 guys who have perfectly uniform cake -- these are the same guys who use two matches to smoke a bowl and never, ever, re-light. The rest of us mere mortals just have what we have and, in the end, we get by and enjoy our smokes despite our obvious limitations.