If memory is correct I think the default for the mach 3 turning CPS file is radius.
Not sure how your going about using Fusion 360, but I would suggest you use the lathe module ie; sketch the part in the correct quadrant for the tool post to be used ,do a revolve to create the solid, set things up correctly in CAM, and define the tool properly.
Simulate to confirm that pathing is appropriate.
May be wrong, but in general, sketch /cam/ post in radius and configure mach appropriately and all should be good.
BTW, attached file should help for defining the lathe tool insert in Fusion.
Have fun,
RICH