We consider a system where two queues share one server. In case of conflict, the first (second) queue is served with probability) beta (1 - beta respectively). We prove strict monotonicity and continuity w.r.t. beta of the mean unfinished work in queues 1 and 2. Restrictive assumptions are avoided as much as possible, by only assuming that the total unfinished work is a regenerative process. Finiteness of the second moment of the length of a regeneration cycle is generally required for continuity. (C) 2017 Elsevier B.V. All rights reserved.