You are incorrect there are LCpls in HCav and the Guards, however they wear two stripes and look like Cpls. So the rank strcture goes:
HCR Ft Gds
LCpl Two Stripes & Crown LCpl Two Stripes
LCOH Three Stripes & Crown LSgt Three Stripes
COH Three Stripes & Crown Sgt Three Stripes
SCpl Four reversed Stripes & Crown CSgt Three Stripes
SCM (WO2) Small Crown CSM Small Crown
RCM (WO1) Royal Arms RSM (WO1) Royal Arms