2 options...but the first thing you needed to do was keep the speed once you realized he was following you - you maintained a climb which just slowed you down and let him close quicker, nose level or down a slight bit for speed.
Option 1: take it nose down harder to speed up back over 300 and keep extending while he closes, when he gets within 800, dump flap, throttle down and get into hard scissors to force his overshoot, get throttle & flap back up full as soon as he's even with you - best if you want to pull him away from the crowd first it, woulda taken him 20 seconds to close
Option 2: need 2k alt for this more agressive move (which you had), get level, when he's 1.5 away roll over 120^ and split S at that angle back into him right across the water, you know he's going to break so plan a very early lead turn into his break and then you can usually have him flying into a rolling scissors which is to your advantage .... he will get away if he wants (if he just goes up keep the speed again in your new direction extending and be ready to do this again), but you get him off your dead 6.
Booz