I am being radar locked on ground but can't do the same to them

So i have been having a problem in top tier because it seems that everyone can radar lock my plane even when i am literaly kissing the ground and they are 10km above me. I am being radar locked and fired missiles even when sitting still on the airfield.

But when i try to do the same (when an enemy retreats to their airfield p.e.) i cannot track them, nor lock, nor nothing. It does not matter which radar mode i use. Not even doppler (which should take the speed difference).

Which is the trick to this? Why it seems that i am the only one unable to radar lock when nose pointing the ground?

I am using the F15E btw