Yes the radius for the turn based mode should be bigger and not only be connected to line of site. Stealth characters feel like they are not part of the game anymore, more like Mythic Trickster breaking the rules. This was already a problem in Divinity 2. This breaks so much, makes stealing no risk at all, traps useless, by locking characters in dialgoue or combat sneak character can easily do whatever they want. There is really no reason to exclude stealthed characters from turn based rules while in the battle zone, I don't have high hopes Larian will fix it as they don't see it as a problem but hopefully a mod will take care of that.

Also this can really bug out the turn base mode. I had a case where my pet wolf wasn't in combat yet, because somehow they didn't see him behind the cupboard or something. So he was allowed more or less to use his jump attack. This screwed with the complete order in which characters took turn. Furthermore some of the characters only had the button shown to skip and could only move them around not even ending their turn. Save and reload helped to solve the problem.