Most plants have a range of sizes. Depending on the size and desired layout planting spaces can vary considerably. The checkboxes have a very narrow range, so most folks check until the entire range is covered. I don't know the western redbud, but the Eastern Redbud (Judas tree) can be anything from a large shrub to a small tree, depending on the environment in which it grows.
Cercis occidentalis, or Western Redbud, can also be grown as a shrub or small tree, multi-trunked or single trunked. It depends on how it's grown what its height and spacing is. It can be grown as a 6-ft shrub OR as a 20-ft tall tree, so the PlantFiles entry must encompass all of those parameters. For example, if it's going to be kept at 10 feet tall it'll be about 10 feet wide, so it should be spaced at least 10 feet apart.
I've added the 6-8ft. and 8-10ft parameters to the "Height" field.
If you have any questions, please don't hesitate to contact us again.