One thing to remember is that tracking imperfections due to period of error are far less looking near north. This is because ra errors do not stats very much on the camera focal plane looking north. But when you look south things fall apart rapidly. So my guess is that you have found the limit of unguided images at 200 mm looking south for your iexos.
That’s just how it works.
Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired