Hi Kuz,
That looks like amp glow to me, it should calibrate out when you process the image.
https://astronomy-imaging-camera.com...-amp-glow.html
I suspect two things, one as I mentioned before pixel ratio the other is that there may be a slight flex in your image train maybe where the filters are attached. Keeping your setting on the camera, could you try a 30sec sub of the horse head nebula without filters and post it ?
Regards,
Vin
