Bulkhead gasket: ridged or flat side against the glass?

[ConsummatePro]

I have this 1" bulkhead and the gasket has a flat and a ridged side. I know the gasket goes on the wet/flanged side for the overflow but which is the better side to put against the glass? Attached image is a leaking bulkhead gasket (after a year) that was originally installed ridged side to glass - I'm replacing it with a new bulkhead and gasket, but wanted to see if I should have done flat side down instead (the leak suggests so!).

 

[fishguy242]

I have always installed flat side to glass.

 

[ca1ore]

I think it probably doesn't matter. I have bought bulkheads with ridges on one side of the gasket, ridges on both sides of the gasket .... and no ridges at all.