In the Wikipedia article about the Second Taiwan Strait crisis that the USA had provided Taiwan air forces with Sidewinder missiles. During clashes with PLA's air force, Sabre equipped with the missiles seem to have scored pretty well.
However, in next conflicts such as the 1971 Indian war, during which Pakistani Air Force used Sabre and Mig-19 jets armed with Sidewinder missiles, it seems not to have performed that well.
Even more, during engagements in Vietnam, the US Air Force and US Navy fighters such as F-4 Phantoms needed many missiles to score one hit. And a gun was asked to reinforce the capability of the F-4 at close range.
So how can we explain the differences of efficiency? I can think of some possibilities:
- Process of evading manoeuvres that allowed Indian and Vietnamese pilots to escape, while PLA's pilots did not have (because they were the first to encounter the missile)?
- Some countermeasures systems? However I did not find such systems on Vietnamese aircrafts.