I would say this is within the range of variation for leucopsis.
- The bird seems to be a first summer (2CY) based on the presence of two ages of tertials. In my experience first year birds often seem to retain some or all tertials through the first winter. An adult would usually have all tertials fresher and the same age. A young bird would be expected to be paler on the mantle and with less white in the coverts than an adult.
- The mantle is rather dark grey (darker than a grey-backed taxon I think) with some darker mottling. The extent of black on the rump is within range for leucopsis I would say.
- The wing coverts are extensively white and lacking any suggestion of dark centres.
- The lesser coverts appear to be fairly dark on the first picture (difficult to judge on other pictures)
- The flanks are white (I think they should be greyer on baicalensis)
It's definitely not ocularis with that head pattern (no eyestripe, black throat doesn't extend onto chin)