Problem with map overlay

I have a problem with the map overlay. I have a main map (from Compass) in tar format. The Locus offline map is set as the overlay. Zoom from 17 to "unlimited." The overlay mode is set to off (I want the map to switch to a more accurate offline map at high zoom levels). When the overlay map is set to Locus Online, everything works as it should, but when it is set to Locus offline, the map does not switch to Locus offline at higher zoom levels.