Dutifully Henri takes whatever position that looks most needed. "Nothing to attack us up here, though. I prefer the front - this bum leg slows me down..." he says, waiting to confirm where the others really want him before going down.

Spoiler: Mechanics
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Henri lacks Darkvision, so he's not best in the very front. He can swim and hold his breath well and is slower than most (Lame curse), so if he's near the front I think that's best. Swim modifier is +5, so here's some rolls in case it matters: (1d20+5)[25], (1d20+5)[22], (1d20+5)[24], (1d20+5)[12], (1d20+5)[6], (1d20+5)[25]