With any kind of protusion made in ordered come the ExtrudedProtrusion_1_FiniteDepth variable when you create a finite depth protusion. Then you expose this variable so to show it in your BOM.Logic.
But the moment you link the protusion to an aother component using key points, you lose this variable and no varaible is shwon for the lentgh of the protusion.
The way around that is to create a PMI and then use that variable.Wich you have to add for every standard parts created extrusions( channels, beams etc...)
Is there a hidden variable or option I don't know about?
IMHO and AFAIK theer is no hiden functionb for that.
What I have done - especially for beams (profiles) - is, that I have put this PMI into the template together with the expose set to on.
Using such a template as sync making the end faces coplanar to others in the ASM will change this PMI automatically, together with angular dimesnions at the ends.
Another approach - I'm using - is to use my main dim macro which will expose this values too.
If the beam is orianed to the main axis YOu will not need to create dims anyway
this macro will do following: