If you have some host groups like:

/hostgroup/foobar/apple/banna

If you have hosts in any of the parents, you can not filter for facts.
eg; you can not use:

host.hostgroup ~ apple
host.hostgroup ~ foobar
host.hostgroup ~ hostgroup

it will only allow calls to
host.hostgroup ~ banana

This means if you have shared hostgroups where multiple teams might share, they can not filter for facts.
eg;

/Corporate/IT/NetworkTeam/
host1
host2
/Corporate/IT/NetworkTeam/foobar
host3
host4

because foobar now exists, searches into /Corporate/IT/NetworkTeam will fail.

The fact searching should be done the same as host searching with:
hostgroup_fullname ~