After watching the Z11 payouts for a while, my leading theory is that the maintenance fee is being multiplied against the payout twice.

For example:
Current 265 units of Z11 payout would be in the range of 0.2235 ZEC
Current maintenance fee is 31.31%, 0.2235 * (1-0.3131) = 0.1535, a number fairly close to the disbursement number Z11 overview page shows at USDT (for some reason)
The maintenance fee appears listed in addition to this at the top of the Z11 market overview.
0.2235 * (1-0.3131)^2 = 0.10545 ZEC, roughly the amount that I get in payment each 24 hrs.

I will start tracking the exact numbers to see if this is accurate.