tokens: K-S tests with respect to the radio properties, and found that the radio sizes of the absorbed and unabsorbed CSO samples could form two populations. In addition, the results of a two-dimensional two-sample K-S test confirmed the possible existence of such two populations. However, we caution that the two-dimensional two-sample K-S test requires a larger number of the absorbed sources (at least twice as many as in the current sample) to be valid. Our results could be interpreted in two ways. It could be that the CSOs with a high intrinsic X-ray absorbing column, N H > 10 23 cm −2 ; 0048+3157, OQ+208, 2021+614, 1511+518, 0108+388) have less evolved radio structures (smaller linear radio size) than X-ray unabsorbed CSOs with the same 5 GHz radio power. Thus, the environment in which a radio source expands might be able to confine the source growth already at the earliest stages of its evolution. This would provide the first observational evidence in the X-ray band that some compact jets may be frustrated by a dense environment and their kinematic ages may be underestimated. An alternative way of explaining the separation visible in Figure 4 is that the X-ray obscured sources have higher radio luminosity than the X-ray unobscured sources for a given radio size. The two factors that drive radio luminosity for a given size of a radio source are environmental density and jet power. Thus, one possible explanation is that the X-ray obscured sources are brighter for a given size because they were born in a denser environment. Another option is that they are brighter than the unobscured CSOs with the same size because they have higher jet power, which is related to central density, through e.g., the accretion rate (e.g., Allen et al. 2006 ; Tchekhovskoy et al. 2011 ; Ghisellini et al. 2014 ), or directly as in the model of Stawarz et al. ( 2008 ). Even though with the current data it is not possible to distinguish between these two explanations, we stress that in both cases the density of the CSO environment plays a key role. Moreover, our results raise a question about the origins of the X-ray emission and the location of the X-ray obscurer. If the CSO X-ray emission originates primarily from an active nucleus that becomes attenuated by obscuring material in the vicinity of the nucleus, then we should also see heavily obscured CSOs with larger radio structures. In contrast, the CSOs in our sample show low intrinsic X-ray absorption for the radio size exceeding a few tens of parsecs. If the CSO X-ray emission is dominated by inverse-Compton emission of the radio lobes (e.g., Stawarz et al. 2008 ; Ostorero et al. 2010 ), then the CSOs would become unobscured once their radio lobes expand beyond the region occupied by the dense material. Thus, it could be that the obscurer is located on scales smaller than a few tens of parsecs. Alternatively, the obscuring material could be destroyed or removed by the expanding radio source. Recently, Ostorero et al.
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