Anna:
You can currently enter '100 Main St B ' or '100 Main St B, Redlands' in the Locate pane and get suggestions that return '100 Main St B' or '100 Main St Unit B, Redlands' depending on how the locator was built. Are you saying that when you select the suggestion when the input does not include a subunit indicator (# or unit, apt, suite....) that it zooms to the wrong location?
If the subunit info 'Unit B' is in a single field in the reference data, the # subunit indicator is required. The best practice is to format the reference data so that the unit type and unit id are in separate fields to get the best results.
If you built your locator with zone (neighborhood, city, state, zip) mapped, do you have 'Match with no zone' set to 'YES'? If you built the locator w/o any zone mapped, the 'Match with no zone' property is set to 'YES' by default. I have seen that when this property is not set correctly that it can affect subaddress search results.
-Shana