Correct exposure for contact printing

I've been wondering about this for a while. When I make contact prints for 35mm and 645 negatives, what is the correct exposure (of the paper)?

I typically make it so that margin of the negatives, the transparent part of the negatives, shows just a little. That is, edges of the film clearly show but transparent part is barely showing. Is this correct?

It seems to me, if I expose more so that transparent part of negatives and margins of paper (out side of film) are equal in darkness (completely black), it's too far exposed. If I expose it less so that transparent part of negatives are clearly less darker than margin of paper, then it's not exposed enough.

Is this correct? What would be the most valuable way to expose it so that I can use it as a guide to make rough judgement for my final prints?

Depends on your purpose. If you want to know if your exposures and development are good, I'd recommend minimum time for maximum black--meaning the unexposed film rebate should be black.

If your exposures are not good, though, you might not be able to tell what's on the neg with minimum time for maximum black, so you might just expose for what gives you the best image, so you can decide what is printable. When exposures vary widely on the same roll, it's not unusual for professional labs to provide two or three proof sheets exposed for different parts of the roll.