The Vibhanga appears to say, consistent with Sutta, the experience of the 1st jhana only has five factors, namely:
If fact, the Saddaṁsuṇātītikathā appears to highlight the logical notion that two parallel mental procedures cannot occur in jhana, namely:12.2. Analysis According to Abhidhamma
12.2.1. Skilful Dhammas Characteristic of the Plane of Form
The four jhānas are: First jhāna, second jhāna, third jhāna, fourth jhāna.
Therein what is first jhāna? Herein at the time when a monk develops the path for rebirth in the plane of form, he, aloof from sense pleasures, See section 205. attains and dwells in earth-totality first jhāna; at that time there is five constituent jhāna (viz.) initial application, sustained application, rapture, pleasure, one-pointedness of consciousness. This is called first jhāna. (As also are) The remaining dhammas associated with the jhāna. (1)
https://suttacentral.net/vb12/en/thittila
Yet the Vibhanga appears to say kayanupassana (which Sutta says includes experiencing the "whole body" and "calming the breathing") is practised in the 1st jhana, as follows:Controverted Point: That one who has attained Jhāna hears sound.
Theravādin: PTS cs 18.8.1If so, it must be equally allowed that he can also see, smell, taste and touch objects. This you deny … You must also allow that he enters Jhāna enjoying auditory consciousness. You deny, for you agree that concentration arises in one who is enjoying mental objects as such? PTS cs 18.8.2 But if you admit that anyone who is actually enjoying sounds hears sounds, and that concentration is the property of one who is actually enjoying mental objects as such, you should not affirm that one in the concentration of Jhāna hears sounds. If you insist that he does, you have here two parallel mental procedures going on at the same time … .
https://suttacentral.net/kv18.8/en/aung-rhysdavids
If the mind is one-pointed in the 1st jhana & only aware of five factors within one sphere of consciousness, how, according to Abhidhammists, does it practise kayanupassana?7.2. The Section Derived from the Abstract Teaching
7.2.1. The First Method
Four Ways of Attending to Mindfulness:
Here a monk, at whatever time, develops the supermundane absorption, which leads out, which goes to decrease (of rebirth), to abandonment of wrong views, to the attainment of the first ground, (where,) quite secluded from sense desires, secluded from unwholesome things, having thinking, reflection, and the happiness and rapture born of seclusion, he dwells, having attained the first absorption, with difficulty in practice and slow deepening of knowledge, and he contemplates (the nature of) the body in the body, and that which at that time is mindfulness, recollection, Right Mindfulness, the Mindfulness factor of Complete Awakening, the Path factor, and what belongs to the Path: this is said to be ‘attending to mindfulness.’
PTS cs 378 And how does a monk dwell contemplating (the nature of) things in (various) things?
Here a monk, at whatever time, develops the supermundane absorption, which leads out, which goes to decrease (of rebirth), to abandonment of wrong views, to the attainment of the first ground, (where,) quite secluded from sense desires, secluded from unwholesome things, having thinking, reflection, and the happiness and rapture born of seclusion, he dwells, having attained the first absorption, with difficulty in practice and slow deepening of knowledge, and he contemplates (the nature of) things in (various) things, and that which at that time is mindfulness, recollection, Right Mindfulness, the Mindfulness factor of Complete Awakening, the Path factor, and what belongs to the Path: this is said to be ‘attending to mindfulness.’
https://suttacentral.net/vb7/en/anandajoti
Thanks