I overtook to leeward — can I luff him up?
Not while Rule 17 applies. If you became overlapped to leeward from clear astern and the overlap began within two of your hull lengths, you may not sail above your proper course while you remain overlapped — and your proper course is the course you'd sail to finish as quickly as possible if the other boat weren't there.
<iframe width="560" height="315" src="https://www.youtube.com/embed/q_bYfQYSJiU" title="Sailing Kiwi" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<p><a href="https://sailing.kiwi.nz/run/rule-17-overlap-from-clear-astern/">Source: Sailing Kiwi</a></p>