9/5 JoB slighty higher than 8/6 JoB?

https://wizardofodds.com/games/video-poker/summary/
9/5 JoB is 98.45%
8/6 JoB is 98.39%

You get flushes more often than boats so i would have thought the higher flush payout of 8/6 JoB would be the one with slightly higher rtp?

Why does 9/5 JoB have a slightly higher return?

It's the strategy. You are probably slightly more likely to get a full house than a flush based on what you are dealt. If you hold a low pair, you obviously can't get a flush, but a full house is in play. Yes, the reverse is true as well with holding two or more suited cards, but what strategy ever calls for holding even 3 suited cards except when they are part of a straight flush?

You actually don't get flushes more often than boats, though. Playing 9/6 basic strategy the hit frequency for a full house is 1 in 86.87 and the frequency for a flush is 1 in 91.14. Thus, dropping the boat by one unit is more of a hit to EV than dropping the flush by one unit.
https://wizardofodds.com/games/video-poker/strategy/a-1-b-74-c-1-d-0-d-1-d-2-d-3-d-4-d-6-d-9-d-25-d-50-d-800/