Shankara's way with analogies (illustrations) has its contradictions but his starting position is that an analogy of its nature cannot be congruent with what it analogises.
Brahma Sutra Bhasya: III.ii.19, 20:
Opponent:The comparison with the reflection of the sun in water cannot be reasonably upheld her (in the case of the Self), since nothing like that is perceived (here). A material thing, such as water, is seen to be clearly separate from and remotely placed from the sun etc. which are themselves material entities (with forms). There it is proper that an image of the sun should be formed. But the Self is not such a material entity (having form); and since It is all-pervasive and non-different from all, It can have no limiting adjuncts either separate or remote from It. Hence this illustration is inapt:
Vedantin: The objection is being remedied:
On the contrary, this illustration is quite apt, inasmuch as the point sought to be illustrated is pertinent. For as between the illustration and the thing illustrated, nobody can show equality in every respect over and above some point of similarity in some way, which is sought to be represented. For if such an all-round similarity exists, the very relation between the illustration and the thing illustrated will fall through. Moreover, this illustration of the reflection of the sun in water is not cooked up by anybody's imagination. But this illustration having been already cited in the scripture, its applicability alone is being pointed out here.
Opponent: Where, again, is the intended point of similarity?
The reply is this: "A participation in increase and decrease”, inasmuch as the reflection of the sun in water increases with the increase of water, and decreases with its reduction, it moves when the water moves, and it differs as the water differs. Thus the sun conforms to the characteristics of the water, but in reality the sun never has these. Thus also from the highest point of view, Brahman, while remaining unchanged and retaining Its sameness, seems to conform to such characteristics as increase and decrease of the limiting adjunct (body), owing to Its entry into such an adjunct as the body. Thus since the illustration and the thing illustrated are both compatible, there is no contradiction.
This is a defence of the utility of the illustration of pure consciousness/Brahman as being like the sun reflected in many vessels of water. It may appear to be many according to the forms of limitation of the vessels but it is the one selfsame sun. When an illustration is taken as alike in every respect to the entity, an aspect of which it seeks to illuminate, then I would say that the analogy has become a metaphor. The curious thing is that Shankara appears to do this himself on occasion. More anon.