Old fashioned MD works on simple changes in pixels. No intelligence at all.
Its divided into squares that use those settings
So Sensitivity is how much of a change in pixel color/contrast triggers MD
Threshold seems to determine a percentage of one of the squares affected.
Always better off using IVS but indoors MD might work for some scenes
Excluding areas is simply unchecking that particular square. Best to clear it all and start from the point of view "where do I care about motion"