Le calibre n'a rien à voir, par contre :
2.7 PROHIBITED HEXES: A Gun cannot occupy an upper building level [EXC: Fortified Buildings and mortars on Rooftops], nor can it occupy a Water Obstacle, crag [EXC: mortars; B17.4], marsh, or Irrigated-paddy (G8.12) unless dm and possessed or in/on a vehicle/boat. Small-Target-Size Guns and AT/INF Guns that are not large targets are the only 5/8" non-vehicular Gun counters that may ever occupy a building/rubble hex [EXC: Rooftop mortars (B23.85); Fortified Building (B23.93)].
L'exception des fortified building est à noter car primordiale dans certains scénarios/campagnes.