Honestly thought it would be a huge hassle, but my first loaf proved me wrong.

So what's the exact oil barrier method you read about?

But a warped heatsink sounds a bit much...

Yeah, that drift thing the_leo mentioned is exactly it. I read a forum post once that called it "inch perfect, mile off" and it stuck with me. You can nail every little section and still end up with a wavy mess.

That's a solid method. I do something similar with my route sheets before I head out. Glance at the whole thing spread on the table instead of reading each address line by line. A missing street just pops out. Saves me from having to double back later.