I believe this wasn't designed in initially because it'd be shrubs excluding shrubs.
Maybe you could send in a drawing where this is definitely needed on a large scale and I can work with you on if permitting shrub area mixes to exclude shrubs is something I can work with our development team on, or if maybe there's a better method.
I'd say using a groundcover concept plant for your mix would be a better solution right now. Is there a reason why the groundcover section isn't working for you?
Really, we've been talking about just simply merging shrub areas and groundcovers into just "Areas". So it'd be Trees, Shrubs and Areas.