<p>This paper studies the influence of the initial number of platforms and the strength of indirect network effects on the profitability of exogenous horizontal mergers in two-sided Cournot markets with linear demands and costs. It compares the benchmark model, without delegation, with the model with strategic delegation where the owner of each platform hires the respective manager through an incentive scheme. It focuses on the existence and properties of the <i>critical proportion</i>, defined as the minimum proportion of firms, out of the total number, that must participate in a merger to be profitable. It is shown that, in both models, the critical proportion decreases with the strength of network effects. In the model without delegation, the critical proportion is increasing in the number of platforms if their number is greater than a threshold, which is decreasing in the strength of network effects. However, in the model with delegation, this occurs only when both the strength of network effects and the initial number of platforms are small enough. If not, the critical proportion may be decreasing.</p>