Our 36" Metro's (fixed deck) have the Exmark mulching kits, we use the wavy mulching blades cutting height to 4". Rarely had problems with blow out or lines. We usually overlap the cut a little, I think that helps the "line" problem.
We'll see some clumping in wet tall grass (on a weekly we usually don't take off more than 3"). We'll leave the clump and come back with a blower (Shindi EB802) and distribute the clump.
I think you'll always have some issues with blowouts, clumping or lines on tall wet grass with any mower, mulch kit or not.