PD of the sources in our sample represented in the first box plot (LSP in blue, above; HSP in red, below). The angular difference between the jet direction and the PA of the sources is represented in the second box plot, with the dashed black line indicating a difference of 0° (LSP in blue, above; HSP in red, below). The black vertical line inside the coloured box marks the median over all observations. The coloured box represents the shortest interval containing 68% of the observations, while the horizontal black lines extend to the full range of values measured across all observations considered. Note: for PKS 2155−304 the coloured box covers the full range, as we only had two observations; for PG 1553+113 and 1ES 0229+200, we only had one observation, so we represent the measurement and its error.