Wireless ad-hoc networks are based on shared medium technology where the nodes arrange access to the medium in a distributed way independent of their current traffic demand. This has the inherent drawback that a node that serves as a relay node for transmissions of multiple neighboring nodes is prone to become a performance "bottleneck". In the present paper such a bottleneck node is modeled via an idealized fluid-flow queueing model in which the complex packet-level behavior (MAC) is represented by a small set of parameters. We extensively validate the model by ad-hoc network simulations that include all the details of the widely used IEEE 802.11 MAC-protocol. Further we show that the overall flow transfer time of a multi-hop flow, which consists of the sum of the delays at the individual nodes, improves by granting a larger share of the medium capacity to the bottleneck node. Such alternative resource sharing strategies can be enforced in real systems by deploying the recently standardized IEEE 802.HE MAC-protocol. We propose a mapping between the parameter settings of IEEE 802. HE and the fluid-flow model, and validate the fluid-flow model and the parameter mapping with detailed system simulations.