Hi Nick
I’ve had a go using ASTAP. It should be said that the two files you provided are not in a form we would normally use for ASTAP so this can’t be accurate.
I get mag. 5.6 and coma of 20′. There’s no way I can see a coma diameter of 29′ in the data using ASTAP.
Measuring the coma diameter is always tricky and I’m sure Comphot will be better at that with the techniques it uses.
It would be interesting to see if the files produced by ASTAP are suitable for use with Comphot though. It can stack on comet or stars, platesolve the star stack and also provide MZERO.
Mark