At first glance, jmr, I notice that your math is incorrect regarding Ho & Hc.
e.g.
Always Remember this nemonic memory jog: The Japanese god of navigation-
HO-MO-TO
that is, whenever Ho is MOre than Hc, then the Intercept is TOward the body. Toward the body is (+) positive and Away from the body is (-) negative.
In your Capella example, Ho is More than Hc, therefore the sign should be (+) positive as the intercept is toward the body. The sign would be negative if Hc were the larger of the two.
Likewise, in your Antares example, Hc is larger than Ho, therefore the sign should be (-) negative as the intercept is away from the body.
I calculated your position fix @ L 48* 22.8'N, Long 005* 02.7'W, a typical "cocked hat" of LOPs.
Same goes for your Arcturus example. The sign is reversed.
