OK, could some nice person try this out.

1] Footage on Track1

2] Apply Mask to ONE side of footage

3] Preview Mask on Internal Preview Monitor - for me Yes

4] Preview Mask on 2nd Preview Monitor - for me Yes

5] Preview Mask on External Monitor - For me NO!

6] Apply Empty Event, directly UNDER masked footage, say T2

7] Preview Mask on External Monitor - For me YES!

8] Remove Empty Event and replace Footage with Generated Media - say Solid White - Apply Mask

9] Can Preview Mask with ALL 3 options, including ExtMon.

Is this correct? And is my statement correct?

A] To Preview MASKED footage on External Monitor I need a Track Layer below

B] To Preview MASKED GenMed on External Monitor does NOT require a Track Layer below

Is this how footage info is shown to ExtMon Preview? It needs an "underlay" track? Not a tad inconsistent?

TIA,

Grazie