To be honest, the more high rank we have more amount we should get it's not only for VIP level but also should be for recent game play. Anyway, I also have another speculation.
Why we got low amount on "Recent Gameplay" because on "Platinum II/III" at that time we got another bonus from "Reload" that's why the recent game play amount is low comparing on Platinum I.
Last month I reached VIP Gold the regular bonus is $100 + $10 for recent gameplay so can we assume that the recent gameplay bonus is 10% of the regular bonus
As you say that is different from other VIP is reload bonus including the amount and duration of the claim. My next target is when the celebration of stake.com's birthday will reach platinum I, usually stake will offer more bonuses.
Vip gold bonus was $100 for me as well, it is standart and reward doubles after gold rank. Regarding additional bonus, it is based on account's last 7 day activity if you lost more than 1% of total wager it gets bigger. I have seen bronze account gets $300 recent gameplay bonus, probably he lost all in single bet then got this rank.