This kinda works for me as well. I drew Aizoon from gacha, then bough Rice Lili (Fritiri...Frita. Fri.... Rice Lily), and after that I drew Soap chan.
As for the gacha - My previous pull was the all bronze pull, and the next one after that (about a week ago) was 2 silvers and 9 bronze.
So I feel ya :P
I wonder if there is some inner treshold that counts how many good pulls you got at some point it peaks out with a great pull, and then it resets back to the bottom and you have to claw your way up via pulls again.