I’ve been continuing my tracking, more out of curiosity than anything else at this point since the devs said they would take a look.
Average: 5.3 per collect
If it checked all 27 kingdoms, that would be 17727 = 4779 kingdom checks with 938 success, or a rate of 19.63%
If it checked 26 kingdoms, that would be 17726 = 4602 kingdom checks with 938 success, or a rate of 20.38%
If it checked 25 kingdoms, that would be 177*25 = 4425 kingdom checks with 938 success, or a rate of 21.19%
Since the expected result is 21.2%, that last number looks VERY likely! So, without having seen any of the code, my guess would be they put a counter to make sure we never got more than 25 kingdoms in one collect (which would make sense down the road, if we had 35+ kingdoms we’d need a cap to keep the rewards from scaling forever). But that counter is instead only checking 25 kingdoms instead of stopping when 25 report success.
(Just for giggles, adding mine to the other data gives a total of over 400 tribute collections, with success rates of 19.70, 20.46, and 21.28 for 27, 26, and 25 kingdoms.)
edit: Another very distinct possibility, the guild bonus is just not doing anything. At 205 collects my rate is 19.93%, if there is no guild bonus you’d expect 20%. And the aggregate data of 430 data points is 19.8%.