We investigate the structure and dynamics of the interaction between high Mach number solar wind flows and a cometary source that is small scale with respect to the cometary ion gyroscales, examples being Grigg-Skjellerup or P/Wirtanen. A series of 2D hybrid simulations are used and we focus on IMF orientations parallel and perpendicular to the simulation plane, these permit or prohibit propagation of modes with a component of k_ parallel to B_0. The perpendicular cases show the onset of magnetosonic turbulence as MA is increased; introducing a parallel B_0 field component significantly changes this turbulence and the apparent shock structure seen on a 'fly-by.' This implies that the Alfv¿n-ion cyclotron mode plays a critical role in the observed structure, and we suggest the relevant mechanism must be resonant growth of such waves in the presence of magnetosonic turbulence from either the unstable ring beam distribution of the pickup ions, or shock reflected solar wind protons. ¿ 2001 American Geophysical Union