Breath getting shorter and shorter Practice : Meditation using breath

I'm practicing sitting meditation using breath according to  Thai Forest Tradition method.

Mentally reciting of "Buddho" .

I practice at home so would like to get help based on my experience so far

I noticed my breath getting shorter and sometimes period of no breath or "nano/very short" size of breath .

When it is a series of "nano/very short" size of breath , mostly what I experience is "waiting" for next "in" breath ? Is this right or where should I concentrate during such occasions ?
This may not be directly related to your tradition but maybe of some value to you or perhaps another reader.

Generally when your bodily fabrications calm down, your breath becomes very short, becomes far apart and even stop for a while. At this point you have to switch to sensations. Generally this will be pleasant sensations but sometimes maybe even gross. If you want to increase your concentration keep it at a point in your upper lip. If not you can choose your whole body.

There are 16 stages of Anapana. This is where you transition at the 5th stage.

Also see: Mindfulness With Breathing : A Manual for Serious Beginners by Buddhadasa Bhikkhu (Author), Santikaro Bhikkhu (Translator) which is a good book to read.

Also another and free books is: Manual of Mindfulness of Breathing (Anapana Dipani) by Ledi Sayadaw Mahathera, Aggamahapandita, D. Litt.