You receive vests. Then vests are converted to sbd or sp. For example your post is at 100 vests after curation rewards. 50 vests goes to sp and 50 vests goes to sbd. The beneficiaries are 25% of your author rewards taken from the Sbd vests. So you get 50 vests in sp and 25 vests in sbd. Example exchange is 1 vest is 1 sp and 1 vest is 0.35 sbd cause of its market price. Do the math. You will really get less. There's nothing wrong with the computation. There's just something that can be done where the beneficiary rewards are taken. Maybe take it from sp instead. Or split it.