Single Fin Template - Thruster set up

Have just picked up a custom board, pretty much gave the shaper carte blanche based on some general details. Basically came back with a 6'6 early 70's single fin outline (wide nose - to pin tail) with a single to double concave thruster set up.

 

Let me start by saying I am loving this board, on my back hand though it rides nice and high but the slightest issue is sometimes I'm wrestling with it a bit as its traveling in a straight line pretty fast and doesnt really want to turn easily (I think this is what tracking means...not sure), having never ridden a single fin is this the norm on backhand? (have twinnies,quad and thruster shapes) and is there a fin set up that may help this (I have M5 size fins set up performance core...100 kilos maybe bigger fins may help?), I've just come off a fishy hybrid swalltail quad after a year so it might be just the different boards. Any similar experience, advice etc....   

 

Forehand its the best board I have ridden.

where's the wide point? could be a variety of different things though

10 inches past the centre towards the nose

That could be your problem, not saying it is, but I put the widepoint back further on thruster setups. It could also be a bunch of other things too. I figured I'd give you a response cause no one else has, but maybe someone else one here can better diagnose your situation. hope this helps you, and glad to hear you like it going frontside though.

It has too many fins.

Put some drivey larger fins on the sides and works a treat.Thanks.