You should try to compare the readings from your unit with other units. I.e. measure the same diamond wires and compare the readings. These gauges dont always give the same measurements between models or even within the same batch.. If you can, set up the boats next to each other and compare the shape of the sails, then start fiddling with diamond tension and try to replicate the shape.
Measuring with a tape measure and a string is very reliable and cheap <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Our masts pre-bend is set up between the tang fittings, and the luff curve is cut into the mainsail in the same way. The part over the upper tangs is not influenced by pre-bend, but by mainsheet and downhaul. If you lack shape in the upper area, it might be that your mainsails luff curve dont match your mast. We have just gone trough the same process with our Tornado mainsail.
When you compared speed/power with your friends, how was your twist and how hard did you sheet your main compared to them? Perhaps they just have better sails for the conditions or did something else to power up their boats? Have you looked critically at your mast rotation and how that changes the sailshape?