ambush is usually set up with enemies spawn circle around your whole squad so i dont think it matters much.
Then again when exploring, your front-liners will be always the one to lead ( like the swamp ) so the party formation as it is now will works as intended.
It only becomes a problem when there is a fixed battle after certain dialouges and you want your main to do the talking instead.
Make it like Pillar Of Eternity, the party formation stay still whenever you engage a conversation with your controlled character BUT the nearest character to that NPC will run up into him instead and you do the talking at the backline.
It works nice and doesn't break the immerson much. If i'm going to talk with a stranger and i'm not good at close combat but good at range, i wont mind talking with the target from few miles away while my bodyguards stand guard in front and ready for trouble.
