Here's how I do it....

I make the fretboard with whatever taper I decide on, then I temporarily attach the neck

Then I use a straight edge and set it in by the amount I want he low E and high E to be from the edge of the fretboard,(typically 1/8") and extend those lines to where the bridge will land and that gives me the exact spacing at the bridge.

Around one half of the nuts that we make may be for reasons that the original nut was not right for the specific player. For example it's very common for our clients to request that a new nut be made with the low e closer to the fretboard edge than the high e. Thumb over low e players and I'm one too and my own guitars when I've replaced a nut are set-up this way. Clapton does this, Carlos too.

Another reason for nut replacements that we do is the spacing is too narrow for a specific player.

I'm bringing this up because so far what I've read here is consideration for and a desire to have a spec or method to determine the distance from the e's to the fret board edge. If that's what you want and you are building acoustics mimic Martin they have it together.

I'll add that on vintage stuff particularly g*bsons g*bson rolled the edges of the fretboard making any spec irreverent in so much as if the string is too close to the edge that rolled edge will want to help the fretted note slide off the fretboard.

So with all this said the original advice that I got way back in the day from Dan E. and what he does and says he does in his books is set the outer e spacing as a function of the neck, fretboard, specific player, playing style if known etc. Dan is not measuring anything nor are we. It's visually done with consideration for al that I've mentioned.

I paid off my mortgage because the nut that came on guitars were not worth keeping according to our clients. As such I would encourage anyone here who wants to get this right to not rigidly subscribe to any spec but to be open minded to player needs, wants, the guitar that you have in front of you and what would work best on it, etc. And it you must have a spec again Martin knows what's happening and has for over 100 years now.

I think the OP is talking about the spacing at the bridge particularly. That's the only way you are going to get the two E strings to be equally spaced along the FB edge. I've almost never built a custom guitar where the spacing at the bridge was not specified first. Once that is set then the bridge has to be placed such that the requirement for the lay of the strings over the FB is met. In most cases it seems people like equidistant but many like to have a bit more room on the High E with low E pushed to the edge. I've even done one the opposite for someone once.