limiting UV point for surface iso-curve extraction

Hi!

I'm trying to simply extract iso-curves from a trimmed surface. However, I can't seem to have control over the limits for the UV point(s) of extraction.

I get that 0 is the first limit, but when I iterate with a number slider, it seems like the other edge of the trimmed surface is somewhere around UV-point e.g. 13,9 instead of just (1,1). (The iso-curve can hopefully be seen as the red lines on the green surface.

How do I extract the UV-value(s) needed to extract iso-curves at the very boarder?

Mostly i might use this max-value to create a domain from what to extract the iso-curves.