The True Being might seem at first glance to be the same as the Inner Being, but it is not. It corresponds to the Central point, The I, or personal self of Psychosynthesis (no.5 in the the Egg Diagram, see comparison with Integral Psychology), except that there is not one but several True Beings, each a distibct purusha, corrsponding to a particyular plane or stratum of existence.
Sri Aurobindo makes several references to this aspect of our nature. The following entries are from some of his letters answering questions from disciples, and appears in Letters on Yoga vol. I pp.307-312). page numbers [thus]
[p.270] The true inner being - the true mental, the true vital, the true physical represent each on its plane and answer to the central being, but the whole of the nature and especially the outer nature does not, nor the ordinary mental, vital or physical personality.
[p.309] The true being mental, vital or subtle physical has always the greater qualities of its plane - it is the Purusha and like the psychic, though in another way, the projection of the Divine, therefore in connection with the higher consciousness and reflects something of it, though it is not altogether that - it is also in tune with the cosmic Truth.
[p.325] ...The true mental being is not the same as the inner mental - true mental, true vital, true physical being means the Purusha of that level freed from the error and ignorant thought and will of the lower Prakriti and directly open to the knowledge and guidance above.