I was referring to the following which is out of the rulebook 5th printing.
Attack Bonus
Your attack bonus with a melee weapon is the following:
Base attack bonus + Strength modifier + size modifier
With a ranged weapon, your attack bonus is the following:
Base attack bonus + Dexterity modifier
+ size modifier + range penalty
Armor Class
Your Armor Class (AC) represents how hard it is for
opponents to land a solid, damaging blow on you. It’s the
attack roll result that an opponent needs to achieve to hit
you. Your AC is equal to the following:
10 + armor bonus + shield bonus + Dexterity modifier +
other modifiers
Note that armor limits your Dexterity bonus, so if you’re
wearing armor, you might not be able to apply your whole
Dexterity bonus to your AC (see Table 6–6).
Sometimes you can’t use your Dexterity bonus (if you
have one). If you can’t react to a blow, you can’t use your
Dexterity bonus to AC. If you don’t have a Dexterity bonus,
your AC does not change.
Other Modifiers: Many other factors modify your AC.
Enhancement Bonuses: Enhancement bonuses apply to
your armor to increase the armor bonus it provides.
Def lection Bonus: Magical def lection effects ward off
attacks and improve your AC.
Natural Armor: If your race has a tough hide, scales, or
thick skin you receive a bonus to your AC.
Dodge Bonuses: Dodge bonuses represent actively
avoiding blows. Any situation that denies you your
Dexterity bonus also denies you dodge bonuses. (Wearing
armor, however, does not limit these bonuses the way it
limits a Dexterity bonus to AC.) Unlike most sorts of
bonuses, dodge bonuses stack with each other.
Size Modifier: You receive a bonus or penalty to your AC
based on your size. See Table 8–1.
Which does make it look like it is used twice. I'm sorry that I am not seeing it as clear as I should, this part of combat has me confounded as it looks like the size mods are used 2 times.