Thanks people!

OT, same issues I struggled with!

I keep the lid frame the same thickness as the box's top frame to make life easier.
Latest technique is to use a marking knife to scribe a line from the back edge of the box frame across the thickness. The line is the same distance it from the back as the frame is thick, plus 1/16" inward.
I then scribe an "X" from the ends of the line corner to corner with the edge of the frame where it meets the inside corner of the box.
Center of the "X" marks the hinge hole, centered and 1/32" in for the lid gap.
Same thing with the lid frame except I skip the 1/16" add-on.
I used to carefully measure and mark the spot, but this way is more accurate and no trying to read a rulers marks.