In Ple4Win the angle 120 degrees is fixed in the source code.

Is it possible to move the fixed angle 120 degrees as an input angle in the SUPANG input table?

According to the helpfile the factor 0.866 (=SIN(120)) is a fixed value:

Ref: Tables Reference > Output Tables > Cross-sectional loading data [CSLOAD] > Data description/Result options / ID: H620511
Ref: Tables Reference > Input Tables > Horizontal soil support / Vertical soil load [LAMBDA] / ID: H610132
Ref: Tables Reference > Input Tables > Horizontal soil support pressure [SOILSUP] / ID: H610152
I have some situations where the horizontal support angle gamma can be greater then 120 degrees if we do a vertical projection of the horizontal support angle 120 degrees for example for hot pipelines (PE-PUR-steel). The angle is greater then 120 degrees on the steel pipe due to the projection. The moment coefficients and deflection coefficients can be calculated according to the 'Geo-Tubomechanica':

f(alpha,beta)=f(gamma,gamma)