I took a stab at the objects location and path based on the lines of bearing above, starting with the objects path and working backwards. I just eyeballed the lines in my drawing, keeping the last angle at 0 degrees, and the intersections at around 30 miles.
I'm assuming the object is another plane traveling about the same speed as the F-18 and in a constant direction, with the ATFLIR looking right down the tailpipe to see the bright IR glare from the engine.
For the object to appear to move from right to left over the clouds, as shown in the Gimbal video, the cloud tops need to be past the intersecting points.
There's another clue from the original video. The object appears to move quickly across the clouds at the beginning, and then slows to a stop at the very end. This means the space between lines of bearing (line of sight) should be larger where they intersect the clouds at first, and get smaller and smaller toward the end.
From my drawing, the object appears to travel about 0.4 NM in 30 seconds across the clouds. The ATFLIR would need to have a tiny field of view to match what we see in the video. Does anyone know the actual FOV when fully zoomed in?
Gimbal is NAR at 2.0 digital zoom so this is probably an FOV of ~0.35 with NAR at 1.0 being 0.7.