thats the nub of it if you didn't change your course and were closing on a collision course , he is Bound" by the rules to give you room to pass , if however although sailing on a reach your course direction was changing as you head up n down with the puffs and your last directional change caused you to head on a colliding course you would have to give him "enough time to take avoiding action " he does not have to anticipate that any course change you make (however small ) would lead to a collison untill such change is made (silly but its the rules )

I've found fastest way of getting round a course is to avoid situations like this if you can , confrontation is often slow even with rights and best kept for one design racing or when a slight slowdown will have no effect on you and the confrontation is tactically worth it .

As an ex mono one design racer its taken me decades to realise this in cat sailing , I now often let port tack monos, cats etc cross me happy in the knowledge I'm heading left because I want to and they are going the wrong way , last thing in that scenario is to force them to tack under you unless of course you want to send them back left and tack off yourself

when meeting boats offwind as above I even at times flogg spi for short while so I can maintain my course same ethos applies , if its a fellow cat your are converging with all they can do is gybe underneath or infront of you , neither good .