Activation of rac-Me2Si(η5-Ind)2ZrMe2 (SBIZrMe2) and sheet models for MAO, (MeAlO)6(Me3Al)4 (6,4), (MeAlO)7(Me3Al)5 (7,5), and (MeAlO)26(Me3Al)9 (26,9) was studied via DFT. These activators can reversibly form an outer-sphere ion-pair (OSIP) [SBIZrMe2AlMe2] [(MeAlO)n(Me3Al)mMe] 3 ([n,m]- = [7,4]-and [26,8]-) or a contact ion-pair (CIP) SBIZrMe-μ-Me-6,4 (2b) from SBIZrMe2. Dissociation of Me3Al from 3 to form CIP SBIZrMe-μ-Me-n,m (2) is generally unfavourable but reversible in toluene continuum. Propene insertion involving CIP 2 features uniformly high barriers of 90-100 kJ mol-1, which are much higher than those experimentally observed for MAO-activated catalysts, though the calculated barriers do track with the coordinating ability of the MAO-based anion, as also suggested by the position of the Me3Al-binding equilibria. The binding of the neutral sheet 6,4 to anion [7,4]- leads to a hybrid anion [13,8]-. The barrier to propene insertion involving CIP SBIZrMe-μ-Me-13,8 (2e) is lower than 60 kJ mol-1. Formation of [SBIZrMe2AlMe2][13,8] (3e) from SBIZrMe2, 7,5 and 6,4 is favorable, though dissociation into 2e and ½ Al2Me6 is not. Simulations of catalyst speciation vs. [Al] at constant [Zr] indicate that the formation of species such as 2e or 3e from two components of MAO explains the high activity observed for MAO-activated metallocene complexes at sufficiently high Al : Zr ratios. Dedicated to Walter Kaminsky (1941-2024).