Hi Mike,
In CTX 1.1, the number of endpoints got converted to capacity units by CTX.  Since CTX couldn't know what type of endpoints would be joining, the required capacity for the meeting would assume the worst case for each endpoint given that bridge type.  This assumption allowed for "endpoint substitutability" so that for example, all endpoints could be 3-screen on the CTMS.  The downside is that CTX 1.1 didn't allow an easy per-meeting way to have finer control of the size of the meeting.
With CTX 1.2, the client specifies exactly the number of screens that are required.  The number of screens gets directly translated into capacity, with one additional capacity per endpoint on the CTMS for the 30 fps data.  CTX then doesn't have to make any "worst case" assumptions for the endpoints.  This number of screens can be consumed by any arbitrary mix of endpoints at meeting time, as long as they don't exceed that total capacity.
- John