The reds didn't have "Siberian riflemen". All their infantry units were "rifles" and some of them happened, naturally, to be Siberian. In this case Copplestone uses it to cover men with the big furry hats mostly worn by Easterners.
Cuprum's flag is pretty generic Red, the only issue being most VTsIK flags were issued quite late in the war. So good for BoB, but not if fighting Czechs in 1918. Also it is a regimental flag. For a lower level unit, something red with gold slogan and/or soviet symbol and the units number on the other side was pretty standard.
Red rifle organisation was triangular all the way down, so three battalions, of three companies.