Unless that MM/broker wants to be fined or lose their license, they'll stick to being close. SEC will look to see if they are sticking close to the deal. My approach would be to record the prior day's volume, calculate 10% of that to sell the next day. It will all average out.
It's simple math. At any given time you cannot exceed 10% of total shares sold at that time during the day. It will always end up being 10% of the total for the day if you simply stick to the simple math. I am really starting to wonder about the intelligence level here. It's not complicated.
I can't believe you find this simple task so confusing. The institution knows what the volume was for a particular day. The total shares sold by all debt holders combined can't exceed 10% of the volume. The shares are in the hands of an institution facilitating this process. No worries.
And the best part? Why would these guys want to negatively affect the pps?