What Exactly Does Defense Do? I Cant Find The Answer In The Core Rule book.

Adds setback dice to the pool.

I would also like to point out that according to the books, defense doesn’t stack, and you can only have one source. (Ie. if your armor provides defense, cover is worthless)

Imo, deleting that rule easily wins the contest for most obvious house rule.

Agreed, the rule as stated in the Genesys Rules (the general system derived from FFGs Star Wars)seem quite alright. If I recall right the way defense is handled in starship combat also makes more sense.

If you want to keep it simple just add all resonable defense up to a maximum of 4.

Genesys caps at 4, just like the starship combat, so the devs seems to agree that a hard cap of 4 works fine and allows to not bother much if something stacks or not.

Well I asked a question to the devs months ago asking about this, no response yet nor update of faq

An important note, there are other things that can add setback die to the pool besides defense, so RAW they stack. Without houserules, defense from armor and defense from cover don't stack. However they both stack with the setback die ranged attacks get targeting a prone character. That's just one example.

The rule is that if something gives defense X doesnt stack, but if it adds to defense it does. A dev answer confused that issue at one point but this has never been followed up or put in the FAQ(we've been waiting for an FAQ update longer than the dev answer as well)