Hi Dan,
The plant label will call out whatever is set to field 1. We have a request on the wishlist already to have the callout default to the first filled out field if Field 1 is blank, but that feature is not yet available.
In the meantime, however, you can revise Field 1 in your plant size preferences for trees to read as simply "Size", and include both caliper and height sizes in there, assigning the caliper sizes to deciduous trees and the height sizes to conifer trees. This is what I normally do.
Here's a link to our plant size preferences page to review your options:
https://www.landfx.com/index.php/docs/admin/office-standards-general/land-fx-preferences/item/1470-plant-sizes-preferences.html
Thanks,
Amanda