Do you get two handed weapon bonus damage with Mythic Power Attack?

Question

Mythic Power Attack says...

When you use Power Attack, you gain a +3 bonus on melee damage rolls instead of +2. When your base attack bonus reaches +4 and every 4 points thereafter, the amount of bonus damage increases by +3 instead of +2.

In addition, the bonus damage from this feat is doubled on a critical hit, before it’s multiplied by the weapon’s critical multiplier.

You can expend one use of mythic power when you activate Power Attack to ignore the penalties on melee attack rolls and combat maneuver checks for 1 minute.

It doesn't mention that two handed weapon (“THW”) damage is increased but the normal Power Attack rules should still apply (i.e. +50% for THW) since the feat doesn't say otherwise.

So wielding THW's should equal +4 damage per -1 to the attack, advancing as normal for each 4 levels gained.

Is that correct?

Answer 1

Yes, you gain +50% from using the weapon two-handed.

Mythic Power Attack is not an independant ability from Power Attack. Rather, it improves your Power Attack, meaning that everything not explicitly mentioned and replaced by the Mythic version of the feat still applies.

This bonus to damage is increased by half (+50%) if you are making an attack with a two-handed weapon, a one handed weapon using two hands, or a primary natural weapon that adds 1-1/2 times your Strength modifier on damage rolls. This bonus to damage is halved (–50%) if you are making an attack with an off-hand weapon or secondary natural weapon.

So if you bonus is normally +2, it is increased to +3 with Mythic Power Attack. Then increased again by +50% if wielding the weapon two-handed, and reduced by 50% if using an off-hand weapon or secondary natural weapon.

Answer 2

To be more precise, it equals to +4.5 damages per -1 to the attack, rounded down: when you reach +4 BAB it becomes +9 damages for -2 to the attack, and so on.