The IDL source code for the Cooling model (Cooling et al., 2001) is available on Brigid Cooling's website, but it currently contains a bug in the function that traces the reconnection line across the magnetopause. If you initiate an X-line at the subsolar point with a strong IMF BY component, uncorrected code will produce an X-line that is straight (viewed in the X-Y plane, see below left), whereas the corrected code produces the expected 'S' shaped X-lines (below right).
The bug arises in the "mergeline" function, which traces a component reconnection line from a specified point. The routine should evaluate the local model magnetosheath and magnetospheric magnetic field directions (Bms and Bgm), calculate the direction perpendicular to the vector (Bms - Bgm), take a step in this direction to trace the X-line and repeat the process. Instead, the code evaluates Bms and Bgm at the initially-specified reconnection site and uses these parameters throughout the function (hence the straight line).
This bug only affects the tracing of the X-line, and the error is only significant for lengthy component X-lines.