May I propose: if you don't see any other solution like drastically changing the game, your last option could be to do both. I explain. During normal gameplay (exploration), the player has a specific speed. Then when there are enemies, the room and characters enter "combat mode" and there you change the rules a bit to mitigate your design problem. The player will understand that in-combat and out-combat rules are different, with different mechanics and different thinking process needed to play.
I was thinking more on the lines of:
- Reducing directional movement penalty (min player speed is 75% of base speed, currently its 50% while moving backwards)
- No stamina cost on actions, while not actively being targeted by an enemy
The combat. non-combat suggestion also works, but I think that would move it away from being action/adventure focused.
Not that it's currently leaning one way or the other, or that I concretely decided what direction it would take, but currently I would nudge it more towards Hades or Rune, then Gothic, or KCD, for example.
Still, good solution if the game should take a more immersive approach.