[TG] [TG11] Placing a waypoint on the sounder screen

[merlin956]

I marked a waypoint from the sounder screen yesterday and I was surprised to see that the point was off to the right of my track.
Referring to the attached picture I placed the skull and crossbones mark on the structure shown on the waypoint. The marker appeared on the GPS screen well to the right of my current track. By the time I took the screenshot, the boat had passed the structure but when I marked it the angle between the boats track and the marker was approximately 90 degrees.
As it turns out the marker was placed exactly over the structure. I made a pass back to check,
As a reference, the distance between the red cross and the rocks symbol is approximately 40 ft, which means the skull and crossbones is about 30 ft off my beam. The water depth was about 60 ft.
As I understand sounder operation it has no idea where in the cone an object is, just that it is somewhere in the cone.
What I don't understand is that the sounder and down vision show what is under the boat. So if the mark was placed on the structure shown on the sounder screen and the mark is on the structure, how could the boat's track be so far away?