Wolverine Siding and Vinyl Carpentry Soffit and Decorative Trim - Manual (Page 46)

Blind Miter
An alternative to a standard blind miter offers support to the
corner without adding material. The measurements shown
for the fold are for a 5" lineal. The same method can be used
with 3-1/2" lineals, but the fold would be changed from 1-1/2"
to 1-3/8".
45
Wolverine Fit and Finish Installation Guide
45ß
Measure at
least 1-1/2"
and notch
with snips
Measure
and
notch 1-1/2"
Dotted line
represents
the position
of a 45˚
mitered
5" lineal
Remove this corner
(dimension dependent
on 1/2" minimum shown
below)
3/4"