The 3s→np resonances were observed to change dramatically in appearance with increasing ionization along the Ar I sequence, and within the 3s→np channel of Ca2+. By applying the Dyson equation method to positive ions for the first time, newly investigated double-electron processes were shown to play a crucial role in the interpretation of the resonance structure. The changes within the resonances result from their position relative to the Cooper minima in the 3s and 3p photoabsorption.