Restrict list of viewable tax codes in iExpenses?

Within iExpenses we have a scenario where when users are itemizing an expense line in the 'Details' section of an expense report they are seeing a list of all tax codes that are enabled for iExpenses across multiple tax regimes. For example we have created tax codes for our Singapore Tax regime which the user can see in iExpenses. Additional to these items the user can also see the codes for New Zealand, Australia, UK etc. We would like to restrict this list so that the user can only view/select tax codes that are relevant to their own tax regime.