Exhaust Manifold Copper Gasket Cross Section

[tommyardin]

If memory serves me the copper gasket washers are compresssion type and squash down and would be flatter and bigger when they come out.
When you put the new ones in smear a bit of grease over the face to the engine it helps them to stay in place when you fit the downpipes and torque the nuts up to correct tightness

Exactly they are indeed meant to compress, I have heard that they are sometimes known as crush Gaskets, when they crush or compress they expand.
The gaskets I got with my S/S down pipes were round in profile and had to dab some grease on them to hold them in plase while I lined the down pipes, They have certainly never leaked at the manifold.