It's highly likely thank your bank would not be able to apply a prepayment at a time different from the regular payment.

At the moment I make my payment, on 10/31, I have no accrued interest. So I pay down some principal. But If I randomly send money on 11/15, they won't apply it to the principal as it's less than the payment due.

Even if they did, it would make very little difference. Make one prepayment on the same payment ticket as the monthly mortgage payment.

It's highly likely that your bank would not be able to apply a prepayment at a time different from the regular payment.

At the moment I make my payment, on 10/31, I have no accrued interest. So I pay down some principal. But If I randomly send money on 11/15, they won't apply it to the principal as it's less than the payment due.

Even if they did, it would make very little difference. Make one prepayment on the same payment ticket as the monthly mortgage payment.