I'm having some difficulty with the Grand Fleet 2 to Grand Admiral conversion formulas and was hoping someone could point out what I'm doing wrong.

For this example I'm going to use the HMS Iron Duke.

BELT ARMOR FORMULA: (GF2 belt armor – 6) x 0.63, round to the nearest integer, then add 2.
GF2 belt armor = 13, so (13 - 6) x 0.63 = 4.41, round to the nearest integer which is 4, then add 2 equals 6.  The Grand Admiral armor rating is 7 so I'm 1 off.

SPEED FORMULA: (GF2 speed x 0.83), round to the nearest integer.
GF2 speed = 4, so (4 x 0.83) = 3.32, round to the nearest integer which is 3.  The Grand Admiral speed is 4, so I'm 1 off.

GUN DICE FORMULA: (GF2 ROF + 2) x (GF2 GUN DAMAGE) x (0.17 for turrets), round to the nearest integer.
13.5” gun data: GF2 ROF = 0, GF2 DAMAGE = 3, so (0 + 2) x (3) x 0.17 = 1.02, round to the nearest integer which is 1.  The Grand Admiral gun dice is 17 so I'm 16 off.

PENETRATION FORMULA:  This one is long so I'll just type it out as I go.
GF2 long range=12
GF2 short range=4
GF2 penetration short range=11
GF2 penetration long range=4
X = (2.96 / long range) = (2.96 / 12) = .24667
Y = (penetration short range / penetration long range) = ( 11 / 4) = 2.75
Z= Y raised to the power of X, (2.75)^(.24667) = 1.28342
GA penetration at range 1 = (GF penetration short range) x 0.63, round to the nearest integer.
GA penetration at range 1 = (11) x 0.63 = 6.93, round to the nearest integer which is 7.  This exactly matches the GA data sheet.  However, now let's look at the range 2 penetration.
GA penetration at range 2 = (GF penetration short range) x 0.63 x Z, round to the nearest integer.
GA penetration at range 2 = (11) x 0.63 x (1.28342) = 8.89, round to the nearest integer which is 9.  The GA value at range 2 is 6 so I'm 3 off.  It continues to get further off at longer ranges.

What am I doing wrong?

Kyle