.

I think that is an interesting observation!

Each practitioner seems to have a unique balance of shamatha and vipassana which is optimal for them, and that balance changes over time as well.

In an ideal world, one sully subdues the hindrances during shamatha and has a deep experience of bliss and calm, which makes the mind receptive for vipassana. What often seems to happen though is that one has a moderately pleasurable experience due to partially subduing the hindrances, but then is left clinging to that incomplete experience and avoiding whatever hindrances remain.

What you could do is try to investigate more closely what it feels like to be spaced out after shamatha. What are you clinging to and what are you avoiding?

Pure concentration?  Some people say many things- as such I would recommend searching the Dho for past conversations. This topic is probably the most discussed on the forum over the years.
use google-
site:www.dharmaoverground.org noting dry jhana concentration [other various key words]

Good luck,
~D

If by "shamatha" you are doing a practice involving intense concentration, you might try relaxing forms of samatha that do not involve intense focus and see how that works. I find intense concentration practices don't work well for me because they cause suppression of thoughts and emotions which produces irritability which is the opposite of what I am looking for. Also mental turbulence is in a large part due to stress and mental fatigue, so relaxing samatha can help produce better concentration during noting. At least that is my experience -  the samatha I do concentrates the mind but it does it by relaxing not forcing.

As for as feeling "spaced out", intense concentration can do that, and intense concentration during noting does that to me too. 

Otherwise you should do what you feel works best for you.  If only doing noting works best for you, then go with that.

I would update my answer with the added information that if you do some form of samatha meditation to quiet your mind before noting it can help in unexpected ways beyond just allowing you to stay focused on noting. One way that noting can work is that when your mind is quiet and you notice sensory experiences, if there isn't a lot of mental activity you just, for example, notice sound and the experience of hearing but there is no thinking about what it means, no thinking about what it means for you, there is just sound and hearing with no self in the middle making an interpretation or commentary. So I think if someone does samatha meditation to quiet their mind before noting they might be more likely to notice that phenomenon - to see how the feeling of self is created by mental activity and to see when the feeling of self is not created. When you have that kind of experience if there is no thinking of self, there is no thinking of attachments or aversions so there is no attachment or aversion associated with the sensory experience (it interrupts the chain of dependent origination between contact and craving) and that is the ultimate goal, not to experience anatta, but to experience non-attachment to end suffering. So samatha can help you quiet down all that mental activity from which attachments arise and the vipassana (noting) can help you become aware of when attachments are present or absent - the two qualities of mind work together to help you cultivate non-attachment to help you stop suffering.