I learned that players often get confused by this (and call GM for help, trapped in TB combat).
I believe that most players expect that the combat mode is determined in the moment when they
enter a location first time. However this is not what happens. Combat mode is determined when
the location is spawned.
For normal encounters it doesn't matter, because location is spawned right before player enters it
- so there is no difference in this case. It makes a difference in case of quest locations.
Quest locations (like straded rust ship, railway gang camp etc) are spawned when players talk to
a quest NPC, in a different place on world map, and often long before the player will visit the quest
location. So it's a bit counter-intuitive, especially if someone does a quest first time or switches
combat mode often.
Therefore I suggest to make combat mode in quest locations to behave in more intuitive way and
set it when player enters the location.