Part of the problem is that CX now has us doing standby in some US ports. That means we are working in the country, not just recovering from the previous sector whilst waiting to operate our next sector out. Other operators don't do that.
CX should deal with any tax issue raised as a result of "working" at their behest while down route or get rid of the mid-pattern reserve. Hope the UK Tax man doesn't take a look at the Gatwick patterns.