Cumulative histogram of the distances to known mass-transferring UCBs. Also plotted is the expected distribution for the local space density measured by van Roestel et al. (2022), extrapolated using a Galactic model with a scale height of 300 pc. The true systems approximately follow the prediction of van Roestel et al. (2022) in the range 150–300 pc, after which incompleteness becomes much more severe. There appears to be an excess at short distances when compared to the prediction (two systems within 100 pc where only one would be predicted), but given the small numbers this is not statistically significant.