Please save my tired lapping hands!

Right...so quick question for anyone with lapping experience. Is there any reason to get the ENTIRE heatsink base flat? I ask because there is one corner of my Big Typhoon that looks like someone slipped when milling it...the stinking thing has about 1mm left to go and I've already been lapping w/ 400 grit for 2 hours.

Since all of the area that could possibly contact the CPU is flat, is there a good reason to continue or could I move on to the CPU?

Well, you shouldn't have to, if it is only a little bit on the edge, so that it wouldn't even tough the IHS, it won't matter at all. Plus, the heat is only in an area about the size of a dime...

Whew...that was my logical assumption, but I just wanted confirmation. I'm going to shine this thing up with 1500 & call it a day...three hours is enough for one stinking heat sink! Thanks.