a. because my car is too low, and b. when I started doing this, race tires had no tread.  Neither front or rear tape measure (or ruler) can get that high up on the tire, and it makes a difference when you are trying to get down to steenths.  I made trammel pins for one of those long Lowe's rulers, but then it draws a crowd as people wonder why is that guy lying on the ground, then jumping up and running around to the other side, no wait now he is running around to this side again...  I finally made a quickie one-man setup with side-of-the-tire toe plates which have slots for two tapes, and yes the tapes are way down low but that is what I use when I am in a hurry.

The 14.5" would be centered on the tire with 7.25" on each side of the center of the wheel.

I've set my toe at .79mm out, half of what Haynes recommends. Originally my toe was set at zero and I've noticed the steering feels a tiny bit sluggish at .79mm out. I may try it at 1.58mm just for reference.

I tried a couple of different camber settings up to 3° negative. I thought I could even out the wear on the inside of the tires and get a little extra milage out of them. At 3° negative the steering was very heavy. I dialed it back to 1.75° and it feels good.

Hmm... I'm using toe plates. It seems to me that the plates are measuring the toe from the center of the wheel to the outside circumference of the wheel; roughly 5" on a 10" wheel. Where does the 14.5" fit in?

The front toe out is set at a certain measurement (1/16", 1.58mm) that should be done at a specific distance between the front and rear measuring points otherwise the toe out does not match what is listed as the correct amount. For instance, the distance between the two measuring "lines" for 10" wheels is 14.5" If more distance between the two measuring lines is used, the toe out will be less than the suggested 1/16" at 14.5". If less distance between the two measuring lines is used (the width of the 10" wheel for example) the toe out will be more than the 1/16" at 14.5".
There is may be different distances than 14.5" for 12" and 13" wheels. Someone else can look them up!

Why can't you just measure the front of the front tires? Pick a tread. Then measure the back of the front tires, using the same designated tread.  Turn the tie rod in or out. Roll the mini back and then forward and measure again. With patience, you will achieve the correct tow out. 

correct.  Got a layout square? Set it behind the front tire, one leg flat on the floor, make a chalk mark at the edge of the square on the tire at about axle height, another on the floor.  Go around to the other side, same thing on the other wheel.  Roll the car forward half a wheel turn, put the square up to the tire mark, mark the floor.  Roll the car back, measure the distance between the rear marks on the floor,  compare with the front marks on the floor, difference is the toe.

Correct.

Haynes sez 1.58 mm toe-out. I assume this means 1.58 mm total—measuring both wheels together, not 1.58 mm per wheel. Correct?