'89 R100RT exhaust header installation

I'm replacing the exhaust headers and I noticed that there is a certain leeway in the positioning of the header inside the head. Specifically, I can insert the header all the way in until it touches, or advance it several millimeters and still be able to tighten the nut. The rest of the exhaust components will also accommodate these two extremes. My guess is to go all the way in, then back out one millimeter or so to allow for differential expansion.
Is anyone aware of the 'right' way to do it? All I read on the topic is to make sure you use the correct anti-seize on the exhaust nuts, which I intend to do.
Thanks,
Marc

Marc -

I don't think it makes much difference. Clearly you want to loosely position all the elements to ensure that you can do a final tighten. As for the header, the exhaust nut and the two washers under it do the sealing to the head.