Hello,
@Götz Echtenacher
“So the short answer to this question is also yes? Or did I miss something? :-)”
Yes, sorry I got carried away with the explanation 
“Would it not makes sense to add another variable where one can simply define the point from which on all the lines will be red?”
I agree, it could be useful information. I will forward it for discussion. Thanks.
“b) the included angle between their two projected lines? (Projected line runs from Camera eye-point, through the Feature; the two projected lines converge, pass close; Tie point is the place where they come closest).”
This is correct, it is an angle created by two projection lines (from two cameras) and the tie point is vertex of the angle.
“If Apical angle is b), the smaller the angle then the more error-prone is the location of the Tie point in the depth map. Is that why the Apical angle setting an ‘at least’ filter? i.e. if set to 3o, Feature matches whose projected lines converge at 2o will not qualify?”
This is also correct.