A suggestion is set your angle units to radians "aunits 3" then (angle pt1 pt2) is always returned in radians no need to convert to degrees. You can set the angle direction clockwise or anti also.
It may be easier to use the pline co-ords and find mid point rather than using getpointatparam. Then just repeat as you step through co-ords check for closed pline so do 1st and last as an extra at end.