A complete AngularJS service with controllers and templates for generating application modals and dialogs for use with Angular-UI-Bootstrap and Twitter Bootstrap
I had tried inserting 'md' into the Plunker for modal that's on the Angular-UI Bootstrap site and it was still coming out large, hence my thought that it wasn't being supported.
If you just allow md value for size you can use md sized dialogs because Angular-UI Bootstrap Modal just skip size attribute if it is not lg or sm.