Hey Chris,
Different Chris..... Sorry about that.
My main is only 1 year old and still stays pretty flat. Did the Pentex this time. Big difference compared to the Mylar. Doesnt move or strecth much at all. I used to have some problems with the twist in the top of the sail. Going to weather requires some pretty serious sheeting and downhaul. After some schooling from Randy I can get it flat as a pancake now. I have bent a clew traveler from sheeting the main so hard. Got 2 clew traveler cars on there now to help spread the load. Are you using some of the wider foam core battens? This makes a difference. Are you a "real" Express (Orig. 6.0 with the lower mast hound and single diamond)? If you are, you have to get the main flat to point well with that huge jib. Took me a long time to figure it out.
Or are you a NA? Different all together than my boat.
Funny you mention the diamonds, spreader rake, tension and pre-bend. I am getting ready to contact him to find out. I'm having them redone before the RTI. I dont actually know what the tension is (never measured it). I'm sure it is probably different than the NA. The spreader rake is 1 1/2". The bottom diamond mount has been moved up about 3" and forward about 1". Also the trap wires are mounted about 2' 6" higher than the main mast hound. Which puts them a foot higher than on the NA (more leverage). Spin hound is about 1' from the top. Mast is just under 32'. I measured it once. 31' 8" I believe. Mast rake is fairly upright at the moment at 18". I am able to swing it back to over 30" with some shrouds I had made locally.
I like the boat but I hate what they have done with the rating. These boats havent been raced much the past 4 or 5 years so why the dramatic change?? Takes some of the fun out of it.
Here is a pic. Dont have many good ones. I'll post one of the Pentex main below as well. It is a notch top (goes to the very top of the mast).
Different topic.......
Hope all that helps some.
Just a little off the thread.

Sorry Doug.
AJ
Express 6.0
Nacra 6.0 Express