The tool is doing what it says, it is finding the point at which the arc intersects the line - however it does so at two places
and has chosen the one you did not expect it to.
The darts are inverted as the line they are based on is rotating 180 degrees around point of origin.
You could base the point from a23 - at the same angle as a21 - a23 ( I presume zero/360 )
then length Line_A23_A23 = SQRT( ((KnownLength_Line_A24_A25)^2) - (( Line_A23_A24)^2)) )