I am confused as to how the ring of transcendent spells from mythic works.
This jade ring is carved in the shape of an ouroboros. Three times per day, the wearer can use it to empower a spell she casts. This grants her a +2 bonus on caster level checks to overcome spell resistance, and increases the save DC of the spell (if any) by 2.
While enhancing a spell this way, the caster can expend one use of mythic power plus an additional use per two spell levels (minimum two uses), to instead cast the mythic version of her spell (though not an augmented version of the mythic spell) as if she knew the mythic version of that spell. This has no effect if the spell doesn't have a mythic version. The save DC increase for being a potent mythic spell stacks with the save DC increase granted by using the ring's power.
For example, if the wearer enhances fireball with this ring, she can expend two uses of mythic power to cast mythic fireball instead (one use plus one use for a 3rd-level spell).
My confusion comes from the example. The way its presented they use only 2 mythic power to power the effect. The item description states that using it requires 1 mythic power and plus one per two spell levels. Since fireball is a 3rd level spell, why did it not require an additional 2 mythic powers for a total cost of 3?
The only way I can understand this to make sense is that the initial cost is allowed to power the spell levels, but this is not said. So is there a mistake in the example or is my solution correct?