Interrupting capacity — the real number
That's not a peak let-through from a backup fuse — the breaker itself takes the full fault. For a 45 mm wide device in the S0 frame, that's serious headroom for high-fault panels like motor control centers or distribution boards downstream of a large transformer.
Mounting position is any — upright, sideways, upside down, doesn't matter. The S0 frame keeps the width at 45 mm, so it fits standard DIN-rail spacing with 50 mm clearance above and below, zero forward or backward clearance needed. For a panel builder that means tight rows without derating.