There should be a lip on the inside to prevent the seal from going too deep. I fear letting the cam gear push the seal in only as far as the cam gear goes could lead to early failure due to the cam sprocket running against the front of the seal. This is one of those cases where wiping a thin film of silicone sealer around the outside edge of the cam seal may be needed even though they don't normally leak, there have been a few cases. Ensure there isn't any knicks or scratches on the front of the cam seal surface and that the front cap isn't loose or any dirt within the two surfaces which would prevent if from clamping down against the outside properly.