I always thought the plastic guard was flimsy. I finally checked it properly when doing the chaine clean/ lube routine and noticed it was not aligned properly to the chain run (in fact very much one sided at the rear).
I run the standard whell/ hub & axle so after some thinking here is what I ended up doing:

put about 3mm spacer behind the front bolt which brings the front out & covers more of the chain while slightly twisting the rear inwards which in turn covers more of the chain at the rear.

Has anyone notice this? Is it designed to be mis-aligned or just a feature?