I have come across an essay ,written by a certain bhikkhu,which might be of interest, it is part of a larger piece but this section seems most relevant for this discussion:
"An enlarged mind vs. An unenlarged mind
The term mahaggata is generally used to refer to a mind that has somehow grown, expanded, become larger, but what this actually means is far from self-evident. One place that we often meet the term is in the stock expression that describes the cultivation of the brahmavihārā , such as here in MN 7.
so mettāsahagatena cetasā ekaṃ disaṃ pharitvā viharati, tathā dutiyaṃ, tathā tatiyaṃ, tathā catutthaṃ. iti uddhamadho tiriyaṃ sabbadhi sabbattatāya sabbāvantaṃ lokaṃ mettāsahagatena cetasā vipulena mahaggatena appamāṇena averena abyāpajjena pharitvā viharati; karuṇāsahagatena cetasā…pe…. muditāsahagatena cetasā…pe…. upekkhāsahagatena cetasā ekaṃ disaṃ pharitvā viharati, tathā dutiyaṃ, tathā tatiyaṃ, tathā catutthaṃ. iti uddhamadho tiriyaṃ sabbadhi sabbattatāya sabbāvantaṃ lokaṃ upekkhāsahagatena cetasā vipulena mahaggatena appamāṇena averena abyāpajjena pharitvā viharati.
He dwells having pervaded one direction with a mind endowed with loving-kindness; likewise the second; likewise the third; likewise the fourth. Thus he dwells having pervaded up-&-down, horizontally, spread out over the entire world with a mind that is endowed with loving-kindness, large, enlarged, unbounded, immeasurable, without anger, without ill-will. He dwells having pervaded one direction with a mind endowed with compassion … sympathetic joy … equanimity; likewise the second; likewise the third; likewise the fourth. Thus he dwells having pervaded up-&-down, horizontally, spread out over the entire world with a mind that is endowed with equanimity, large, enlarged, unbounded, immeasurable, without anger, without ill-will.
MN 7
Cultivating mettā means pervading the mind with the intention of good-will for all beings. The phenomenon of ‘person’ (which arises for the puthujjana , and includes ‘this-person-who-I-am’) and the phenomenon of ‘individual’ are simply phenomena which arise. They arise against a background which is the mind, and this will have certain underlying or latent tendencies (unless one is an arahat ) which pull the experience in certain directions. For instance, as we have seen, a mind infected with paṭighānusaya (the underlying tendency to ill-will) will be affected by the arisen phenomena and will tend towards an aversive response. One is more likely to perceive the unpleasant and to be repelled. One who cultivates mettā works at changing the underlying tendencies. By pervading the background (i.e. the mind) with a sense of acceptance, benevolence, amity, whenever the phenomenon of other people (or the phenomenon of this person) arises, this will be manifested on a background of mettā . The tendency will be to respond to people on the basis of this quality of mettā .
The Buddha encouraged his disciples to develop a mind endowed with loving-kindness ( mettāsahagata citta ), but it is important to understand that one cannot do this without first knowing what the mind is. It is only once one has discerned what citta is, once one has grasped the nimitta of citta, that it becomes possible to endow it with certain qualities such as loving-kindness, compassion, or simply to brighten or gladden it. How could it be possible for one to gladden the mind without knowing what the mind is? It is perhaps worth noting here that this also applies to ānāpānassati . Before one can develop mindfulness of in-&-out breathing, one first needs to have discerned the phenomenon of mind.
‘cittapaṭisaṃvedī assasissāmī’ti sikkhati, ‘cittapaṭisaṃvedī passasissāmī’ti sikkhati; ‘abhippamodayaṃ cittaṃ assasissāmī’ti sikkhati, ‘abhippamodayaṃ cittaṃ passasissāmī’ti sikkhati; ‘samādahaṃ cittaṃ assasissāmī’ti sikkhati, ‘samādahaṃ cittaṃ passasissāmī’ti sikkhati; ‘vimocayaṃ cittaṃ assasissāmī’ti sikkhati, ‘vimocayaṃ cittaṃ passasissāmī’ti sikkhati.
One trains thus: “I will breathe in as one who experiences the mind”. One trains thus: “I will breathe out as one who experiences the mind”. One trains thus: “I will breathe in having gladdened the mind”. One trains thus: “I will breathe out having gladdened the mind”. One trains thus: “I will breathe in having composed the mind”. One trains thus: “I will breathe out having composed the mind”. One trains thus: “I will breathe in having liberated the mind”. One trains thus: “I will breathe out having liberated the mind”.
MN 118
When the quality of mettā is fully established one knows that any being that one might encounter—any being at all—can only be encountered within this field of mettā . One now knows that it is not possible to experience any being (whether, in the case of the puthujjana , my self or others, or whether, in the case of the arahat , this individual set of the five aggregates or five aggregates externally) without them being there within this context of good-will. The mettā is now all-pervasive, unbounded, infinite. It is in this way that the mind can be reckoned in terms of its size and can be described as vipula (large, extensive, abundant), mahaggata (enlarged, expanded, become great) or even appamāṇa (immeasurable, unbounded, unlimited, infinite). When one has discerned the mind, and knows that the mind is always the larger background within which more particular phenomena arise, then one knows that whatever particular thing I attend to, the mind is always bigger than that. In this sense, the infinity of the mind can be known. That is why the arahat , one who has fully understood the mind, can be described as one with an immeasurable mind."