The same thing happened in the thread listed below. This seems to be a common issue. Simply put, if the master cylinder does not have enough volume, it will not fully release the throw out bearing.
https://lateral-g.net/forums/showthread.php4?t=40386
I run into the same thing with people putting over sized calipers on and then having very little braking. Hope this helps and I know chasing it is frustrating.