Tailward polarisation electric field as a log₁₀ fraction of the solar wind electric field (colour scale) as a function of the column ion density [m⁻²] and the ratio of the solar wind to comet magnetic field strength. Black contour lines indicate the log₁₀ number of data points to fall into the corresponding parameter space. We use density estimates obtained by the MIP instrument. White lines indicate the limits where the tailward electric field is 10% of the solar wind electric field.