The things you describe are the UNI-HIGH and UNI-LOW modes, usually you want UNI-LAST.
They are in the Voices page, in the right hand side under zones.
These modes really shine when you are creating a multi patch with several zones, you can have a bass sound holding down the lowest note of a chord using UNI-LOW, or a lead sound riding on the top note with UNI-HIGH.