Both screens have to ideally be set to the same resolution. - See these threads...
https://www.feldoncentral.com/forums...55&#post108755
https://www.feldoncentral.com/forums...25&#post109825
https://www.feldoncentral.com/forums...26&#post109126
Do you have the option to set both your screens to the same
vertical resolution? - If so try that.
Edit: I see in your second post, (posted whilst I was looking up those links), that you have now done that!