Ultimatum Notable Rewards Wave 10 and 13

I am doing with Ultimatum a lot recently. My setup is: all Ultimatum passives and gilded scarab. I equally tried wave 10 and wave 13 setups. In the end, I realized all notable drops(mageblood divination cards, divines, rare uniques) are specially from wave 8 and 11. I literally didn't get anything valuable from wave 13. I got additional +2 waves from scarab and passive skill. It looks like there is fixed wave 10 and wave 13 notable drop. Do anyone have backup data on this?. If this is correct. I'll switch winged scarap and unallocate wave 13 key stone.