When you're behind and you manage to get the guy infront to instigate a tacking-duel i.e. everytime you tack they tack to cover (keep yourself between the oppositon and the next mark scenario) the trick is to stay cool.
When handled correctly you are pretty much in the dominant role... tack when you want to, don't rush, tack on those tiny headers, take care to tack "properly" in big waves, roll tack "appropriately.. what you will find is that when the "opposition" tacks, he won't be tacking on a header or will slam tack into a wave or will do a bad/fumbled tack...
As each tack is executed you stand the chance of gaining a boat-length, maybe a little less maybe a lot more... get the tacking duel started early and by the top of the beat you should be in control... then the reverse happens..
When he tacks, as long as there is a decent gap between you 10 boat-lengths+, you have time to tack in a controlled manner, on the little header, smoothly and can negate the benefit the aggressor has...
phew..hope that makes sense!
sailing boat soulsailor