So, let's say I'm a Hurler Barbarian (+10 increment) throwing a deer knife (20' increment) using Startoss Shower.
I've got the Strong Arm, Supple Wrist trait (+10' on the first attack of the round, and only if I can move before throwing).
Pretty straightforward so far. 40' increment on the initial throw, 30' on the bounces.
But eventually, I manage to get Weapon Style Mastery and Unfolding Wind Strike, doubling my increment while in my styles. Does the doubling apply before or after the addition?
And a couple levels later, I get Raging Hurler, which also doubles my increment, but only when raging. So what's the range increment of my knife at this point?
You would add before doubling.
The second multiplier would work just like other multipliers, so you add the base (after your additions) again.
2 x2 incriments = x3.
So for a final, 120' on your first one, 90 on the others.