"Let them 'sell' the need to address this indication."
The problem is that B and X are not approved to treat the same indication. B's indication is to replace Enoxaparin for the duration of the hospital stay plus for a period after discharge. X does not replace Eno, it gets prescribed at discharge only. As you have personal experience, some hospitals send patients home with a bag full of hypo's preloaded with eno, but this is an off label prescription and the hospitals don't get to charge for administering those shots. I don't see how this helps B, because PTLA still has to figure out how to get hospitals to break the Lovenox habit and use B instead.
It may increase A use as these are patients otherwise treatment naïve to anticoagulants and with comorbidities, a profile that could result in X induced bleeds.