Snapping to reference geometry

I can never seem to get sketch elements to align/snap to geometry related to solid bodies created in other operations or with other elements created in the same sketch. I use the align tool often and it usually works but if, for example I just want two different lines to intersect at the midpoint of one of the lines I can’t seem to get them to snap in place appropriately. Am I missing something?

Just to be clear, I understand I can use a dimensional constraint but I’d like one line to be on midpoint no matter the length of the other line.