searching for non-virtual machines....

Hi, I'm trying to figure out how to use Tower Search (
https://docs.ansible.com/ansible-tower/3.4.0/html/userguide/search_sort.html
) either ad-hoc or as a smart inventory to pick up all the non-virtual
machines.

Navigating to my host list I can see that two variables are being
populated that relate to it:

virtual: vmware
is_virtual: 'true'

however tryin to use either one in search yields no success. Going
through the API I can see that those vars are double-JSON encrypted
inside the "variables" . So what's the right way of accessing those
values? I've tried "variables.is_virtual:false" and
"variables.virtual:!vmware" even tried to pick up only the virtuals just
to get rid of extra conditions - no dice. What's the right method to
accessing the "variables" field for the host from within smart inventory
or just a search?