You are quoting numbers which may or may not be right for the screen configuration.
If you use the auto-field of view, you will not lose any vertical, at all as long as the resolution is set correctly for the multi-monitor configuration.
I just watched HiTech do a dynamic window size change and it did not lose a single pixel in the vertical going from 4:3 to 48:10 aspect ratios.
If you are losing vertical, then your field of view is not set correctly, and that is why the auto-field of view option exists.