for the calc, i dont know.
gelerdria + storm has 50% default boss bonus attack, if you put 3 ak you got another 75% bonus attack
for the extra atk multiplier it goes like 100% x 100% x 100% x 100% (bonus ATK (boss,weap%,phyisical%, etc) x Racial modifier x Elemental Modifier x Size Modifier)
if you use 3 AK it will go like: 225 x 100 x 100 x 100 = 225% damage increase
if you use 2 AK 1 mino: 200 x 100 x 100 x 115 = 230% damage increase
1 AK 2 mino : 175 x 100 x 100 x 130 = 227.5 rounded down 227% damage increase
soo mix and match accordingly!
also Kingbird (10% ranged damage) behave differently, be careful!