MAINT: fix slopes when plane is flipped
MAINT: fix slopes when plane is flipped

SiLab-Bonn/testbeam_analysis,SiLab-Bonn/testbeam_analysis,SiLab-Bonn/testbeam_analysis,YannickDieter/testbeam_analysis,YannickDieter/testbeam_analysis,YannickDieter/testbeam_analysis,SiLab-Bonn/testbeam_analysis,YannickDieter/testbeam_analysis