Yeah it really looks like Larian multiplies the weapon damage die with the number of Sneak Attack dice you get as a rogue at a certain level.
That would explain the notion behind that formula.
*Sigh* another thing that supports that Larian doesn't want to use DnD rules.
It's not like the rules for sneak attack damage would be very complicated, but they just didn't want them in the game.
As to why, I really would like to know.
