Some Zenith tracking advice

[symesie04]

Just after a little advice please gents. I understood it that the closer to the zenith the object you are tracking the less accurate your alignment needs to be within reason. Have i got that the wrong way round?

Im still very much getting to grips with my astrotrac and loving it. However i seem to be having some issues with star trails on objects near the zenith. I feel my polar alignment is quite good, i have manged 5 mins subs of andromeda at 200mm and the stars are pretty good. However when imaging cygnus areas at 50mm 300 secs or shorter i get star trails around the edges of the image. I at first thought maybe it was the lens and so have tried various others, i have stopped down and used wide open to no avail. Unfortunately right at the moment i cant attach anything to give examples but wondered if anyone has some ideas anyway.

Cheers