The calculated distance (air line) between Sv. Ana v Slov. Goricah and Postojna is approximately 99 miles respectively 159 kilometers.
By car or train, the actual journey to Postojna is certainly longer, as only the direct route (as the crow flies) between Sv. Ana v Slov. Goricah and Postojna has been calculated here.
Air line (approximately)
159 kilometers
86 nautical miles