It's pretty fubared.
RAW, here's how it works.
Step 1: You need to figure out how your armor accessories are applied. "Armor accessories" are things that give +x/+x. Helmets, shields, and PPP are examples. FFBA is not an accessory. The way they work is they modify the rating of some other armor you are wearing.
For example, if you have FFBA full, PPP full, and a lined coat, you can apply the PPP to the FFBA, which makes the FFBA is 8/8 and the lined coat is 6/4. Or you can apply it to the Line Coat, and so the FFBA is 6/2 and the lined coat is 8/10. Or you can apply the PPP helmet to FFBA and the rest of PPP to the coat, so the FFBA is 6/4 and the coat is 8/8. Technically, you also halve the armor of armor accessories applied to FFBA for encumbrance purposes, but very few GMs will let that fly.
Step 2: Look at all the ratings of the base armor pieces you have. If you are wearing any piece of softweave armor, you reduce that rating by your Strength for encumbrance purposes - even if the softweaved piece is not the same as the piece that has the highest rating. If you have a tie for highest rating, your universe crashes. It's also unclear what happens with FFBA - do you halve then subtract strength or vice versa?
Obviously not many GMs will actually run this as written. The most common houseruled version (which is likely RAI) is "of all the armor and armor accessories you are wearing with Softweave, locate the one with the highest single rating, ties broken by the decision of the character. Reduce that particular rating by Strength for encumbrance purrposes."
Strength is always 3 in these examples.
Example: You are wearing an Urban Explorer Jumpsuit with Softweave and nothing else. RAW, the universe crashes. Most people will let it count as either 3/6 or 6/3, your choice.
Example: You are wearing a non-Softweaved Lined Coat (6/4) and Softweaved Clothing (0/0). RAW, your lined coat counts as 3/4. Most people will rule that Softweave does nothing here.
Example: You are wearing a Softweaved Lined Coat, non-Softweaved Form Fitting Body Armor, and non-Softweaved PPP. The PPP is all applied to the Lined Coat. RAW, you have an 8/10 piece and a 6/2 piece, the highest single rating is 10, so it counts as 7 and your armor is considered 11/8 for encumbrance purposes. The most common interpretation here is going to be that the lined coat counts as 3/4, though, and thus your total is considered 8/11 instead.
Example: You are wearing a Lined Coat (non-softweave) and a Softweave Helmet. RAW, you are considered to be wearing a single 7/6 piece, so the 7 counts as a 4 for encumbrance and you are considered to have 4/6 armor for encumbrance. Most people will rule that the helmet counts as +1/+0 for encumbrance and so your overall armor counts as 7/4 for encumbrance.
Example: you are wearing a Softweaved Form-fitting Body Armor and Softweaved Lined Coat. RAW, there are two things with 6 ratings so the universe crashes. Most people will let you pick one or the other. It's also unclear how this works with FFBA and order of operations, so you could count as 6/5 or 7/5 (if you pick the FFBA, depending on ruling), or 9/3 (if you pick the lined coat).