Autoposition

HI all I am new to the forum and am from Canada, it seems like a great place to communicate and learn.

I am currently using topcon hiper ga base and rover gps (and a fc2500 data collector). I am noticing a difference from when I set up over a known control point and when I use the "auto position" function in the start base screen.

When I set up over a known point and proceed to another point it gives me an error of roughly 10cm in the easting every time. When I set the base up over a random spot and correct to a control point everything seems to work fine.

Not sure if anyone can help me with this but any insight would be great.

Thanks