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The sum rate of spectrum-sharing in decentralized and self-organizing wireless networks is investigated in this paper. Such networks pose the following two fundamental challenges: 1) cochannel interference and 2) the hidden node problem. For a slotted shared wireless medium, where resources are partitioned into time-frequency slots, time-multiplexed receiver initiated busy burst (BB) transmissions solve these problems by establishing an exclusion region around an active receiver by means of receiver feedback. The size of this exclusion region is controlled by an interference threshold that determines whether a user is allowed to transmit on a specific time-frequency resource unit. We propose a novel approach for setting the interference thresholds based on a heuristic derived for a two-link network. First, for two-links, the optimum threshold value is derived that maximizes the sum rate. Second, for multiple links, the new heuristic threshold that only relies on locally available information is derived. It is demonstrated via simulations that heuristic thresholding achieves superior sum rate compared to a fixed system-wide threshold. To complement simulation results, an analytical approach is developed to approximate the probability density function (pdf) of the sum of the interferers in BB setting with fixed threshold with a cumulant-based shifted log normal fitting method.