I have no problems with Hugin when doing normal panorama work using my
panorama head, the stuff Hugin is designed for. This application
introduces non-linear issues though, possibly micro-variations in film
curl etc, the micro-metric scale makes it hard to provide "error-free"
input, and on top of that the grainy structure makes seams in slightly
mismatching low contrast areas visible.

As said in the previous post, I now think it is hard to solve this
problem without having a rubber-sheeting or similar non-linear
correction model to handle residual errors. A software designed for
stitching aerial photographs for maps may be the thing, still
searching for something suitable and that works on a tight budget
though.

The trick I did with yaw/pitch corrections and small FOV was just a
"hack" to deal with residual errors the yaw/pitch that the optimizer
finds is not real, but sometimes it works and improves matching
without bad side effects. At first I thought it almost always worked,
but now after more testing I've been forced to change my mind.