Jody, a couple of things to consider...
The saddle is longer than the actual spread of the strings. So, if you measure the angle as a difference between the compensation for the high E and low E strings, you will get a different angle if you measure that at the actual location of those two strings at the saddle, on the one hand, or at the ends of the saddle, on the other. In other words, if the END of the saddle at the low E end is 3mm further back than the END of the saddle at the high E end, then the difference in compensation between the two strings themselves will be less than 3mm; one person's angle will also be different from another's depending on the length of the saddle (how far it extends beyond the spread of the strings).
Likewise, if you determine the angle that way, the angle of the saddle will be different if the string spacing is different. The tighter the string spacing, the sharper the angle will be.
Another interesting thing is that the difference people use between the compensation of the two E strings varies pretty widely. The smallest difference I've heard (and which I've used myself successfully) is 1.7mm. That's substantially less of a saddle angle than you have with a 3mm difference, like Tony uses - and Robbie goes as far as 3.5mm. Assuming Tony's and Robbie's guitars intonate well - and I know mine do - that suggests that there is a surprising amount of wiggle room there.
When I built my saddle slotting jig, I figured out that an average string spacing and a compensation difference between the high and low Es of about 1.75mm gives me a 2 degree angle on the saddle. I decided to go with that angle on all my guitars (for the time being, anyway), and I figure that, with the intonation of each individual string that I do by shaping the top of my fairly thick saddle, I can get each string spot on, even with a range of string spacings on different guitars. So far, so good. I do use a thick saddle (though I'm thinking of going a bit thinner), because I like the idea of more string contact on the saddle, in addition to the ample room for intonating each string.
I also put a 10 degree back tilt on the saddle, so that the force of the strings breaking over the saddle is pushing the saddle more straight down onto the floor of its slot, rather than tending to push it forward against the front wall of the slot. There are those who claim this improves sound; I haven't reached my own conclusion about that yet, but the logic of it makes sense to me, especially with regard to the use of an undersaddle pickup.
In fact, if I hadn't been designing a jig that had to account for the added complication in geometry dictated by the 10 degree back tilt, I probably wouldn't have settled on the 2 degree angle at all. If you don't use the back tilt, then making a jig that allows you to change the saddle angle from one guitar to the next is a simple matter. But making a jig where the saddle angle can be changed but the back tilt and slot depth remain constant was beyond my little brain's capacity. Anyway, I don't anticipate having a problem with the 2 degree angle, and if I do, I'll cross that bridge when I come to it.
I hope this is helpful.
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