There is a relatively unhighlighted connection between the fourth base of awareness and the five hindering contractions to immersion. The five are skeptical doubt, restlessness and remorse, dullness, sensual desire, aversion. In discourses on immersion, the key to access immersion is seclusion from those five contradictions. In AN 9:36 it reads:

Take a mendicant who, quite secluded from sensual pleasures, secluded from unskillful qualities, enters and remains in the first absorption.

In 22 DN the fourth base of awareness is described to include awareness of these five contractions and how they have arisen, how they can cease. So, if one wants to gain immersion, but has doubt or feels dullness, that very doubt is a hindrance to that immersion in the first place. If one can become aware of this doubt, dependent upon what it arises and ceases, one cultivates a path towards seclusion from it, which is one of the five seclusions to immersion.

Generally, immersion can be taught as a result of simply watching the breath. In mindful or aware contact meditation, the importance of how the breath is contacted, dependent upon which mental state and effort, is important. Without that, the reason watching the breath can work is at some point one tunes into a wholesome effort and and confidence develops that immersion is developing. This confidence, and thus seclusion from the hindrance skeptical doubt, is built by proxy through rounds of effort and experience eventually leading somewhere.

But rather than relying on developing confidence by proxy of a lot of effort, there can be awareness about doubt to gain immersion. And then to awarefully cultivate seclusion from that doubt into a wholesome contact as a basis for immersion. One then further develops seclusion and confidence away from that doubt until the dependently arisen path away from it is fully understood. That path is the stream away from it, the first shore, that awareness has been raised onto.