Jumpy popup positions

[Peter Chr. Gram]

I use the same calendar on several pages and in popup windows. However I have a hard time vertically positioning the calendar (y factor).

With the same settings the calendar's vertical position differs a lot from page to page. 

(The calendar icon is positioned in a HTML-table)

Any ideas to how I can get a better control over the position?

(PS: do not suggest replacing HTML-table with CSS)