Greater Power Attack

I’m using a 14th liv two-hand fighter with 5 Mythic tiers that allow him to add the Mythic Feat: Power Attack (Mythic) to Power Attack. When a two-handed fighter makes a full-attack with a two-handed weapon, his damage roll with Strength 32 (mod +11) so reach:

11 x 1.5 = 16 for the first strike and 11 x 2 = 22 for all attacks after the first (due to Backswing) and adding Power Attack: (without consider other feats or abilities or weapon)

11 x 1.5=16 + 4.5 (or 9, or 13, or 18 if using Power Attack maximum) for the first strike and 11 x 2 = 22 + 4.5 (or 9, or 13, or 18 if using Power Attack maximum) for all attacks after the first (due to Backswing)

And what’s happen when he reaches 15° liv and gain Greater Power Attack?

from the text I understand: 11 x 2 =22 + 4.5 (or 9, or 13, or 18 if using Power Attack at max) for all 4 attacks

It’s all correct?

Thank you