Thanks, Mario
Yes, I have read somewhere before and might find a website you describe a few years ago.
Honestly, I want some actual data from real Alembics.
After deep thinking, I'm planning like this.
Set fatboy fist at the 90% place of scale length, second lay rear side MXY side by side, then neck MXY put apart the same distance from another MXY as my 34inch Epic4.
The interval between two MXYs is 101mm (center to center).
I intend to take over two basses.
So, fatboy makes the datum point relatively affected by scale reduction, but MXYs interval not.
The results are the neck MXY at 82.5%, bridge MXY at 94.5% of the scale.
I'm sorry but the idea is not firm yet.
Shinichiro