Must be more kondishuns tu yer problem.
As me understand yer werds...yu hav a rite triangel with a vertikal & horizontal side.
Me thank yu sae yu draw semiserkel from middel av the vertikal side with radius=hite/2
So semiserkel go out horizontal from the top point, kerv arount tile hit the rite triangel at bottom
Me tried a sampel av this & its kleer the serkel hit the diagonal neer the bottom:
NOT at middel. Me just did I-ball werk...its WAE off.