Your mental diagnostics are sound.  I’ll try to report back in with some exact CC values, but I have the feeling that is going to be reverb-dependent (variable per the selected algorithm).  The areas for subjectively ‘short decay’ are often in a narrow range of values.  And there are also differing lengths of maximum (sometimes minimum) Decay lengths.  Shouldn’t affect the Infinite & Freeze CC values all that much.

One great thing about the MC6 Pro is the vast number of options available for CC control.  Very powerful: CC Value Scroll, LFO, Step Sequencer …out any kind of port.  Try a Press & Release Action Type switching, for the path I think you’re headed in.  CC values from a mid-size reverb Decay to INF/Freeze.  You can ‘sample’ the reverb, hold the INF/Freeze on it, then smoothy decay out of it upon release.  It’s a versatile performance technique.