It is a simple trig function for those without a cad program or the time to draft it.

Measure the width of the fuselage at the leading edge (LE) and trailing edge (TE) of the V-tail.

Take the V-tail angle, divide it by 2 and subtract from 90. This the the angle of the V-tail above the horizontal plane. We will call this angle alpha in degrees.

So the difference in height of the leading edge and trailing edge is as follows:

The height difference on the fuselage side = [(LE-TE)/2] x Tangent (alpha)

This is the amount the TE must be lower than the LE on the fuselage side when the wing is mounted and at zero-zero.