How are you bringing in the kPa to display? I tested a couple by manually adding it in without a binding and also linking to the engUnit of a tag and both did not display it in all uppercase. You could always have the first field be bound directly to the tag and a second tag set to the engUnit property.
Bi-directionality can't work with a transformed value. You are changing the value that would be on a tag and it wouldn't be able to work back to the source value.