It looks like you want to use scheduled with best effort instead of guaranteed perhaps because you want to take advantage of overbooking on the resource pool?  In any case, you are correctly inferring what the proper behavior should be.  Rather than needing to calculate the number of screens for your given scheduled meeting + endpoints, you can simply provide a sufficiently large value (e.g. 100) for your minScreens value and CTX will do a minimum of that value and the calculated value for the meeting.  Doing so will guarantee that when/if the meeting happens, it will have the required capacity for all participants allocated at the beginning of the meeting.
- John