(m,k)-firm or weakly-hard real-time (WHRT) guarantee allows to guarantee the deadline meeting of m among any k consecutive task invocations or message transmissions. This kind of guarantee is becoming attractive as it proposes an alternative between hard real-time guarantee (case of m = k) and soft (or probabilistic) real-time guarantee (with p=m/k with m, k ® ¥) and allows more effective utilisation of server resources (processor for task processing or bandwidth for message transmission). A scheduling algorithm called DBP (Distance Based Priority) has been proposed to handle the (m,k)-firm constraint. This paper shows that DBP combined with EDF (EDF for making choice among the tasks/messages of the same priority assigned by DBP) can not always provide good performance in a MIQSS (Multiple input queues single server) model. The raison is that DBP assignment is only based on the distance to failure state of each individual source under (m,k) constraint. It does not take into account neither the source timing parameters (period, deadline, service time in server) nor its relationship with other sources sharing the same server. Taking into account these additional parameters, a modification of DBP called matrix-DBP is proposed to improve its performance. The simulation results show the effectiveness of this proposal.