We've had both a 1978 retractable gear G-103 Twin Astir and a 1986 G-103 Twin II Acro (well, not really "acro" since the AD) in the fleet. The old one had fuselage side statics and a short tail mounted pitot while the newer one has the pitot head, static ports and T.E. venturi on a single multi-probe on the leading edge of the vertical stabilizer. They were both better at maintaining an airspeed reading in a slip than gliders with nose pot pitots I've flown (L-13, L-23, ASW-15b etc.) Sounds like it may be just that one ship. What setup does your ship use for the pitot/static system?