The critical behaviour of statistical models with long-range interactions exhibits distinct regimes as a function of $rho$, the power of the interaction strength decay. For $rho$ large enough, $rho>rho_{rm sr}$, the critical behaviour is observed to coincide with that of the short-range model. However, there are controversial aspects regarding this picture, one of which is the value of the short-range threshold $rho_{rm sr}$ in the case of the long-range XY model in two dimensions. We study the 2d XY model on the {it diluted} graph, a sparse graph obtained from the 2d lattice by rewiring links with probability decaying with the Euclidean distance of the lattice as $|r|^{-rho}$, which is expected to feature the same critical behavior of the long range model. Through Monte Carlo sampling and finite-size analysis of the spontaneous magnetisation and of the Binder cumulant, we present numerical evidence that $rho_{rm sr}=4$. According to such a result, one expects the model to belong to the Berezinskii-Kosterlitz-Thouless (BKT) universality class for $rhoge 4$, and to present a $2^{nd}$-order transition for $rho<4$.
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