Trying to find the best non leaking 2.5" collector gaskets for my RK Sport headers.

The y-pipe flange is is totally flat and the mating header flange has a raised ridge which appears to be build up of weld that was machined flat I assume to make a better seal.

I have used flat aluminum with decent results, but still leaked a very slight amount.

I bought some copper ones today that have a raised ridge but I don't like the way they are fitting. The three corners of the flange are torqued down but there is still a lot of gap where the bolts are not present. It seems like the ridge is not crushing or conforming. It clearly looks like the flanges are bending some. Maybe they are over torqued.

Can anyone recommend the best collector gasket for the headers that I described? Should I get a graphite/steel type that is more conforming?