If I use Strength in Subtlety's action at a battlefield, can I resolve it's trait targeting someone not at that battlefield (since it is a trait, and not apparently restricted by location/presence, from what I can find in the CR)?
Strength in Subtlety
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
If I use Strength in Subtlety's action at a battlefield, can I resolve it's trait targeting someone not at that battlefield (since it is a trait, and not apparently restricted by location/presence, from what I can find in the CR)?
Yes, you may. The Rules of Location only constrain the targets of actions.