thanks, adam!
yer it stops at 22-4. it looks like 22-2, 22-3, and 22-4 all share about the same bonus as the kill screen. barrel, pies, and elevators give you enough time to clear them if youre fast enough, but the rivets dont. its best to immediately run up and grab the left rivet hammer in hopes of some good spawns. hopefully ill get that chance next run