Edge length of 135 (45) degree hook bar too short when filleting?

When using the fillet command and selecting the correct pin size (radius size), I noticed the **Edge** length of a 135 (45) degree hook bar is always too short when filleting?

It's fine for 90 degree bent bars, just not when 135 degrees, such as the two hooks in a closed stirrup.

Drawing two lines (or a polyline) then i choose the radius (20mm for 40mm pin), then fillet.

How can I get this to represent correctly?