I have a question. I started practicing yoga reading book by E. R. Ram Kumar - 'Heal Yourself With Yoga.' In it he says when doing prarnayama to inhale, retain, and exhale in a time ratio of 1:4:2. I also added an additional thing to it that is to exhale and empty my lungs and pull my stomach back. How long do I have to hold this position? Is the same time as retaining the breath taken in enough? That means a time ratio of 1:4:2:4. Is this correct?