Your terminology unfortunately confuses me. To me, "layover" and "stopover" are synonymous. What you call a "layover" is what airlines call a "connection." Sorry for any confusion.
No worries. The way I was using the terms were:
STOPOVER - more than 24 hour stop.
LAYOVER - less than 24 hour stop, as scheduled explicitly by the traveler. Counts toward MPM.
CONNECTION - less than 24 hour stop (although potentially in rare cases more) as scheduled by the airline between two points. Different from LAYOVER because it does not count in the MPM, at least for many airlines. Not sure about Delta.