Sorry but i am not good in math
i have 1 XPY in 1 hashstaker
the reward is paid out to my XPY wallet on zencloud, it does not stay in the hashstaker so it cannot compound the interest, the interest is flat and paid on the initial deposit only
HashStaker payouts are just that - payouts. It has nothing to do with staking, and if I understand correctly Prime staking wasn't even working properly until now. So you're just getting paid from GAW's coin stash, and yes it doesn't compound.
Prime Controllers are special wallets that GAW owns and those have a compounding staking rate. Theoretically HashStaker payouts should be coming from that, but see above.