I would say that calculating the curve with combination of Lense & no lense would be halfway inbetween...
ie completly flat surface is perfect for a projector without anamorphic lense, and based on what your projector image curve actually makes with the lense system as the maximum curve. ( can be calculated, but I measured with the 'stick method' )
so for me:
projector: panasonic ae700
lense: DIY anamorphic set for 2.35:!
screen: DIY curved PVC/foam gain of around 1.2
initially I put the lense up and setup as correctly as I could, and gave me an equal curve horizontally top and bottom.
Used a long pole that reached vertically from the ground to above the top of the projected image and marked the top and bottom of the image on the stick at the center (horizontaly) of the image. I then moved the stick to the Left hand edge of the image and moved the stick towards the projector until the marks lined up with the image. Then I measured the distance to the wall, this gave me the "rise".
from that you can calculate the radius ( for me it was around 9.4 meters I think) , but doesn't matter as I can calculate the circle from the width of image I want and the 100mm rise from the L & R edges.
you can calculate the radius from the Width of screen and rise with:
screen curvature radius = r
Screen width = w
screen rise = sr
r=( (w/2)^2 + sr^2) / (2 * sr )
And with that formula you can calculate any point on the curve.
see this post for the worksheet that Mark.J.Foster kindly worked out.http://www.avsforum.com/avs-vb/showthread.php?t=586590
for me thats in cm:
R = ((274/2)^2 + 10^2) / (2 * 10 )
R = ((18436 + 100) / (20 )
R = 926.8cm
So if you want optimal for both, then that iwll be half of the curve, so make it 50mm rise on each side of the screen, to get an average of the 2.
but for me I'm going to leave lense in place and compress the image for 16:9, as you allways have to have some loss somewhere at difference aspects, but minimal because I'll be mostly viewing dvd's, and sometimes Hidef dvb sports channel occasionally.
So really you need to look at your usage...
>%50 in 1.76 format then keep it flat and remove lense when not needed, and have a good masking when you do
50/50 1.76/2.35 then maybe half the rise for your curved screen and good masking
>%50 in 2.35 format then use mostly lense and 2.35 full rise for your curve, and remove lense with good masking, or use the compress image to 4:3 for less quality 1.76 format (loose %30 horizontal pixels)
Thats my take on that.