Excellent overview of the deeper stages of meditation by Yogani (author of the AYP Enlightenment Series), at the AYP Forum.
Any or all of the variations in experience (and mantra) you mentioned above are fine. The particulars are not important. What is important is the intention.
If the intention is to favor the mantra when we realize we are off it, and allow it to go however it will (patterns do not matter), then this will lead to losing (refinement) of the mantra, which is the cultivation of inner silence. This is the process we keep repeating easily for the allotted time of our meditation session.
If the intention is to analyze, control, question, modify, report, etc., this will not be meditation. And it will not matter what system of meditation we may be following. All meditation procedures involve systematically going beyond the object, whether it be mantra, breath, nada, vision, sensation, concept, or whatever.
It is dharana (attention on an object), becoming dhyana (natural dissolving of the object), becoming samadhi (absorption in inner silence). These are the last three limbs of the eight limbs of yoga, which gives an indication of how important this process is in the overall scheme of yoga. Samyama also utilizes these three limbs, in a different way.
Obviously, choosing and sticking with a method of meditation is important. We can’t cross the vast ocean of samsara (impurity/illusion) in two or more boats at the same time. It is all about developing and maintaining consistency in practice over time.
This is the only question we need to be asking ourselves about meditation: “Am I in a consistent practice with a proven method?” All the rest is diversion.
We can never, ever, ever! put it in a mental bottle. Meditation is about emptying the bottle, and dissolving the bottle. So all this talk is not very relevant – only to get rid of doubts about the simplicity of sitting down and doing it every day. That’s all. If it is going to keep going in endless circles of mental analysis, etc., don’t expect any serious meditator to take that ride with you for long. It is not about creating complexity. It is about releasing into simplicity. Meditation is for that.
The guru is in you.