FaT activation distance vs. TDC range - Q

[Keelbuster]

I've had a long-standing wonder about the FaT pattern activation setting. When you set the TDC range, that's the current range, and the TDC computes the course of the torpedo. The run-distance until impact of the torpedo will be shorter than the range set in TDC, because the range you set is the hypotenuse (at least for a 90 AoB shot). However, I fear the the FaT activation range is a real run distance and hence if you set the FaT range to the same setting as the TDC range, the pattern will always activate beyond the target. While this isn't a massive problem for shots that are close to 90 AoB (and you do want the pattern to activate slightly beyond the target so that it has the best chance for a hit on the first pass), it would be good to have a way to set the FaT activation so it would reliably be say...150-200m past the predicted impact point.

Does this make sense? Am I using the FaT wrong?