If you really want to read up on Coma:
https://www.telescope-optics.net/coma.htm
To quote from "Telescopes Eyepieces Astrographs" p172
For a 200mm f4.5 Newtonian ....only 7.5 arcmin off axis the coma has grown to over three times the Airy disk.
p175 they discuss wide field observing with an eyepiece (27mm) giving a 1.5 degree FOV (0.75 deg off axis) - the coma, towards the edge, would be 28 arcsec - "which is larger than the disk of Mars at it's closest"