lack of precsion in crystal reflectivity far from bragg angle

[srio]

S4 gives too high reflectivity at angles far fron Bragg angle.
TODO: revise the reflectivity at high angles.

Bug case: https://raw.githubusercontent.com/oasys-esrf-kit/modelling_team_scripts_and_workspaces/refs/heads/main/id11/id11_v1.ows

Spectrum (at slit) in log

After 2 crystals with S4 (buggy):

with S3 (ok)