The 22 coach limit for LHB rakes is mainly because of the lack of sufficiently long platforms at most stations.
Just looking at the weight of the coaches, LHB coaches are lighter than ICF coaches. A 24 coach LHB rake will be lighter than a 24 coach ICF rake.
So, a 23 coach LHB rake is not really testing the limits of a P7. In fact, for a P7 that is regularly hauling 24 coach ICF rakes, it is actually easier to haul an LHB rake of the same length.