Haha I'm just doing that atm, to be honest I had 54 degrees at one point during our attempts at calculating so I assumed it was from this lol.
At the moment I'm getting 68 degrees from 26-27.5 with a perpendicular 7th fret, 3mm equal overhang, 44mm and 63.297mm string spacings.
This gives me 158
The only way I can think of getting between 18-26 degrees is making the perpendicular fret around the 20th fret to reduce the angle.