Hierarchical Mobile IPv6 (HMIPv6) was proposed by Internet Engineering Task Force (IETF) to reduce signalling cost by localising the mobility signalling traffic of Mobile Nodes (MNs). However, certain MNs still generate excessive signalling overhead, due to their ping pong movement at borders of different Mobility Anchor Point (MAP) domains. In this paper, an algorithm is proposed, to effectively reduce the handover signalling overhead in the network. A cost function was developed and allocated to Access Routers (ARs) in then network, by taking into account several parameters. The proposed algorithm spreads the domain of each MAP to its adjacent MAP(s) domains by selecting boundary ARs one by one, based on their cost values, and creating overlapping regions between the domains. The performance in the new network structure created by the proposed algorithm is evaluated against a single MAP per domain HMIPv6 access network. A comparison simulation study illustrates a significant improved performance in the network is obtained, in terms of average rate of inter-area handover, whilst balance in terms of bandwidth utilisation among MAPs is maintained.