SSR4: During the setup, the Russian Player may convert
two hexes of his choice to stone rubble, and two other
non-open ground hexes can be converted to open ground,
by use of the open-ground overlays.
The rules allow rubble only in building hexes. Also, the General article on Rubble clarifies that no vehicle may enter a Rubble hex, despite the Q&A to the contrary.
However, the SSR allows 'two hexes of his choice'. Since SSR by definition do not follow the rules, the designer may have wanted to override the rule and allow placement in any hex.
Should Rubble placement be limited to only building hexes or any hex? what is your reasoning and effect on play.