Going by the Lua I believe that moving spread has finally been implemented. It's been there at the release of the game as far as I know (I only joined in a 2-3 months later), but was quickly removed.

I wish the Lua hook still worked because I want to properly verify something this important. If moving spread is indeed used, then there's a table going from 0.5 to 2.5 with the usual index shifts due to weapon + mods. Except that the values are not shown anywhere in the game.

If the player is moving, add (moving spread - 1) to the stance value. Put another way, let moving spread go from -0.5 to 1.5. So if the moving spread is low enough, subtract up to 0.5 from the stance value. In the worst case, add 1.5 to the stance value. As the player must be on the move however, the stance values are rather usually around 3 anyway (twice as much for shotguns even). So the effect is not that pronounced and pretty hard to verify without Lua hook.