We now have a ton of evidence across multiple threads (Kingdom Tribute - Is Guild Tribute Chance Bonus being accounted for? Bug?, plus my own data that I’ve been collecting but hadn’t published yet) that the bonus is multiplicative. I agree that it’s incredibly misleading. It’s also kind of pitiful compared to the yellow statue bonus.
[Math follows, assuming 27 level-10 kingdoms at 3+ stars, and both red and yellow statues maxed]
I am not sure one additional gem every three collections (and 3.2 tribute points in bonus tribute each time) is equal to 5.4 tribute points every time you collect. It does provide another way to compare how much the devs think a single gem is worth: 6.6 tribute points (165 gold, 27 souls, or 6.6 glory).