Using your 8:03 plot and 8:05 plot and drawing a straight line between I show the placard at 471 feet NE of the flight path.
It seems to me that your 8:03 plot is too far west. If you note on the yellow map, the 8:03 plot is very close to the west-to-east halfway point between 8:02 and 8:05. I'm talking about the distance east that 8:05 is to 8:02.
Using your points, the 8:03 plot is about 20% of the distance east between 8:02 and 8:05.
I realize this is not very clear. My point is that it appears that your 8:03 plot is too far west.