Confusing visibility rules on moving map

Two airfields of same type (LOAG, LOAU) have different visibility depending on the scale factor.

The next picture shows that at the scale of 15nm the left airfield (LOAG) is visible at least with the simple airfield sign without a name, the right one is not.

Zooming in until 6nm the 2nd one (LOAU) becomes visible at the right hand side

Zooming out again the right one stays visible until about 10nm