Split Shot / Splitting Steel interaction

The description of the two is Split on Impact respective on target.
I assume this means the same.
Do they overwrite each other, or is it additive?

And how does it interact with piercing?
Do they split again on the next target/impact?

Since projectiles split on impact it does increase boss damage too, at least with Nimiz, right?

Could I calculate this in PoB, by adding 2 projectiles for an average of 2 assumed piercings * (2 splits * 50% chance)?

Two different skills
Two different gems

Which specifical skill are you asking does what to what?

Look up projectile behavior priority order.

Hi

Splitting Steel and wanted to apply Split Shot on the tree.
As i understand it: 50% chance for a second projectile on Split means Nimiz gets even stronger when the extra Projectiles return.

Splitting > Piercing > Forking > Chaining > Returning

But only if the Splitting Steel Skill Gem itself doesnt overrule/cancel the 50% or that Explosion changes anything.
F.e.: Will Nimiz allow the projectiles to return after their original end, or will it prolong their journey?

Idk you can test it though