I have figured out the answer to this. Support pool = 3 per defense GB level in the guild + guild level support pool bonus
Example: say I am a 5 man guild, and each of us has a level 10 deal castle and level 10 SBC, with a level 0 guild. My guild's support pool is 300.
In the iron age, it takes 75 support pool to fill up your HQ to 75% atk/def
Then, all adjacent hexes receive what's left, and split it amongst themselves. Let's say my HQ has 2 adjacent sectors. Then they will each receive 50 of my guild's support pool. (300 - 75 - 100 = 125 remaining)
Then, all adjacent hexes to those hexes split what's left. Let's say there are 5 adjacent hexes to those 2. Then they will split the 125 equally, and each receive 25% bonus.
Now, let's repeat this scenario in the CA. CA has a support factor of 3. Now all hexes use up 3x as much support pool to grant the same bonus.
CA: My HQ still receives 75% attack, but instead uses up 225 support pool (75 remaining)
The two adjacent hexes split the remainder (75/2 = 37.5 per hex -> 37.5 / 3 = 12.5 = 13)
So with a support pool of 300 my CA HQ will receive a 75% bonus, the two adjacent hexes receive 13% each (I think), and all other hexes get 0% bonus.
Let's repeat in the PE. 300 / 6 = 50% to the HQ. No other sectors get any bonus.
Hope this helps.