Also wasn't sure what you meant by the "line going down the centers."
A 9' long pole arced to 42" high should give you about 5' of width, but I don't think a Fibraplex pole (my guess at what you ordered) can withstand that tight an arc. Even if you use Easton carbon tent poles, or Easton axis nano arrow shafts with the least spine available, I don't think you will be able to push the pole tips to be only 42" apart without snapping the pole either then or later. Suggest you either add an elbow fixture at the top, and/or go with a 5' width between the pole ends and use a high quality, low spine, carbon shaft.
If you decide to use the Axis Nano 350s, I would be glad to send you a few Easton alloy inserts which will serve as external ferrules (I had to buy a min order of 100).
It sounds like your design is similar in outside shape to the TT Scarp 1, only a little smaller in width, but longer and about the same height. So it might interest you to know that the Scarp1 sil-nylon outer, without the carbon struts, weighs about 19.2 oz. The sil nylon is probably around 1.3-1.4 oz/sq yd, so .6 oz cuben would cut that weight in a little more than half, and that's assuming you have the same amount of zippers, the same heavier weight pole sleeve, and about the same number of attachment points as the Scarp.
To get the surface area of the single wall tent, you can use Cadware, or if you are a computer illiterate like me, you can compute the surface area of two large half cones (1 cone total) which reach out at both ends to the point where your roof line and sides would converge if extended out to a point. Then compute the surface area of the smaller cone which = the nonexistant extended portion, and subtract it from the total. You can also build a scale model skeleton with music wire and foam or similar board and cord, and break the surface area down into as close as you can get to triangular and rectangular pieces which you can compute the areas of and add up. You might try several ways to be sure you are in the zone with the surface area. Also suggest you actually weigh the cuben. I have found that the weight can be somewhat more than specified. Then you will have the canopy weight.
Unfortunately, what adds up are the little odds and ends, like zippers, pole sleeves, attachment points, reinforcements, hems, etc. So you have to figure those in if you are set on knowing the weight in advance (I just use the least and the lightest and accept the total addition to the weight). It sounds like you will be adding something akin to reversed snowskirts also, and that will add weight. With all the stakes, assume you will go for the lighest and best Ti you can find.
I suppose you could also spring for a TN Photon, excellently reviewed on this site.
Hope this is of some help.
Sam Farrington, Chocorua NH