Payouts are not uniform across blocks. It could be that the third block had a lot more fees or maybe there were less miners contributing hashrate or for some reason the other ehash holders cashed out early, leaving more reward for this share to claim.

I did not intend to make it higher, that was actually a mistake lol. It is actually even higher now in the slide deck to clear the red line. In practice, hashrate tends to remain steady and rewards look very similar across blocks with PPLNS even if the blocks come faster than expected.