I recall what you describe as Progressive MOR and if memory is correct, it was similar to KNX FM back in the middle to late 1970s.
For me, I recall the format called "Mellow Rock". It was what I liked to call the more acoustic side of album rock but the long playlists, album tract centered format with atypical Album Rock Radio's soft speaking jocks back announcing long sets of music, centered on those very artists mentioned as Progressive MOR. In fact, In Dallas, it was 102.9 that went to the format in the mid-1970s after KDTX sold. I was hoping Mellow Rock would hit Dallas after a trip to Orange County, California where what was KORJ FM, K-Orange, was mellow rock and KNX FM was going strong.
I really enjoyed the short time the McKinney, Texas station was Mellow Rock. It seems they had abandoned their Beautiful Music format for the Mellow Rock sound. They were automated but played some great stuff. You heard plenty of early Fogelberg, things like Let It Grow by Clapton, CSN&Y, James Taylor, etc. They were all 'deep' tracks with a well known song about every 15 minutes. It didn't last too long as the station sold and went all hit top 40. I doubt they had too many listeners given their coverage and the fact that Dallas had yet to expand out to Plano, much less what was a farm town of 10,000 back then, McKinney, miles of open country from the northern reaches of metro Dallas. I lived in Mesquite then and it was hard to catch very clearly there.