it depends on how the vendor decide to perform the resource allocation. It is not defined (afaik) in the 3GPP.
So for example:
4 MS onto 2 PDCH.
Why only 2 PDCH ? Let’s assume it is because the other timeslots are already busy with TCH.
Possible implementation:
each MS has 2 PDCH only (even though they have MS capability to support 4 PDCHs), because they can’t have more : the BSS will allocate only 2PDCH to each of them.
Now, of course, those 2 PDCH are the same for each MS. So each PDCH provides a possible link for 4 different MS. There are 4 MS multiplexed onto each PDCH.
Since not all MS are receiving data at the same time, one MS could have 100% max throughput over 2 PDCH during few seconds…