Hey you have an icon and not all of us do so we need to catch up!
Doing by eye isn't a bad thing when you're setting up your own screen. You can tailor the screen to your projector, setting, and personal preferences. We deal more with making recommendations across a wide range of projectors, so having a screen that we know will work equally as well with projector A as with projector B is an important factor.
I've seen some DIY screens (even some commercial screens for that matter) where the developer obviously preferred a cooler image so their screen was a bit biased towards cool (blue), or some that were a warm screen. Then I've seen some people rave, while other's loathed the screen. If a screen is cool and a person prefers a warm image, then of course they aren't going to be happy with it.
Also if we can get the materials that you use I'm sure mech will do some readings on it for you.