I was complaining here early on but got my last 5 atmas in like 2 hours.
Guess it was my lucky day.

But I know how it feels to grind for 4h and get nothing. =/


My suggestion is:
If you kill Garuda HM (or EM) without Echo boost, you get one (or two) of the green atmas.
If you kill Titan HM (or EM) without Echo boost, you get one (or two) of the yellow atmas.
If you kill Ifrit HM (or EM) without Echo boost, you get one (or two) of the red atmas.
If you kill Leviathan HM (or EM) without Echo boost, you get one (or two) of the blue atmas.