force field of vision

[clankill3r]

I try to match a beamer with something to projection map on.
The beames has a given fov, is there any easy way to match this with fspy? Right now I have to be really precise on the lines I set and check the outcome for the fov.

Also, as a future request, it would be nice if you could force a field of vision and that fspy tries to come up with the closest matching result possible.