If you did it eliptically, like with a belt sander or a CNC shaper, the change would be perfect and gradual, technically beginning even before the first fret, with your nut slot or nut end of the fretboard at 9.5". I like the first three frets to be at 9.5 and then begin to flatten. Conversely, I don't like to be at my final radius until the last fret. That is to say, don't make the top 5 frets all 16", because the most dramatic effect of a compound radius is in the bending of those last frets. But to make it simple, you can figure about four frets per radius. Of course there will only be one fret that is actually that radius, because the rest will be a transition. But about every four frets you should begin to use another block. Again, remember, 1-24 are 9.5", then transition to 4-24 10.5" or 11", then 8-24 at 12", etc.
The slope phenomenon you're talking about isn't a curved slope at all. It is the very essence of a compond radius. Think about it. Your fretboard will either be thinner in the middle on the high frets
, or if you did it in reverse, thinner on the outsides of the low frets. What the straight edge should show is actually a straight line IF you follow in the direction of the strings. Yes, on a blueprint type drawing the G and D strings would get closer to the plane of the outer E's. That is what is supposed to happen. And the bridge will be set for a 16"-20" radius for proper action. Most Floyds are pretty flat, and just about everything else besides tune-o-matics are adjustable.
There's no pics of that machine, at least you can't see it in any of the pics of the shop. Picture a playground swing where one of the cables is shorter than the other. It will swing ****eyed. Back and to the left, then forward and to the left. I think you'd have to use pipe or something else solid like he does, so it didn't pivot on the axis where it was attatched.