Here's a big surprise. At 12 feet away you should have a huge screen to be able to see a 1080i picture well. It is all about being able to see a 1080i picture from 12ft. with 20/20 vision and good contrast. Here's the math, so hang on.
20/20 vision allows you to resolve 60 line pairs per degree of arc. A rule of thumb, literally, is that if you were to draw 60 lines on your thumbnail and hold it at arms length (how could you hold it out longer?) you could resolve the lines if you had 20/20 vision.
But at 60 lines/degree you would have almost no contrast. A picture would lose it's punch. You need to go down to about 22-30 line pairs/degree to get good contrast.
A 1080i picture is 1920 pixels wide. That is 960 line pairs.
Haha that's very good, I hear people bragging about megapixels but how many megapixels can our human vision actually process.
So to have 22-30 lines per degree with 960 line pairs you need a screen that is between 32 and 43 degrees wide, and at 12 feet there are about 2.5" per degree (12ft x 2 x 3.14/360). That gives you a screen that is between 80 and 109 inches wide. But since screens are measured diag. a screen that wide would be 92 to 125 inches.
So there you have it. Tell your wife you need a 100" screen (Panasonic makes a 103").
BTW - My wife didn't buy it either. Mine is 37", but it was worth a shot.