Chances of receiving epic and unique?

I've heard from friends that Premium Miracle Cubes have a better chance at getting Epic or Unique. Is it (somewhat) true or are they just lucky?

I would say that it is true.
I normal cube to epic, then I Master cube to legendary.
The total amount of cubes from rare to legendary is, for me, about 12~15 cubes.
But as I Said earlier, the amount it takes for the Lines I want is a different story...