I have never come across anything in which Yogananda stated or wrote this is how I practice kriya and techniques are not given in the book which has been stated numerous times. So, basically who knows what he personally practiced unless one witnessed and practiced with him. And he were to explain in detail.
I think more on the subject can be found by googling " Ennio Nimis". This person was in search of the original kriya and was involved with learning some techniques from Yogananda’s organization (SRF) however, the techniques stated I believe are the modified/simpler techniques given as it was/is believed westerners are unable to perform some of the techniques/steps. (ie, Kechari)
I think Yogananda practiced differently from what he gave to many of his followers simply because he could accomplish the techniques like kechari while others could not.
Avatar has given a good explanation of the use of the pranayam. Decarbonization.
makes things harder.