You could say, of course, that the ground of all analogies is the eternal relationship of the Father and the Son and the fact that the Son is the Image of the Father. You could say that the covenant is grounded in the eternal life of God rather than in relationship between God and the world which is founded upon the hypostatic union. But these things need not be set against each other:
- the eternal relationship of Father and Son
- any intra-trinitarian covenant which you may choose to assert
- the hypostatic union
- the Father's act of creation by the Word ...
all of these (perspectivally!) are grounds of analogies and grounds of the covenant. But in creation, the primary (though not the chronologically first), the original, and the principial "relating" of the uncreated and the created is the hypostatic union.
This is how we find it in one of the longer paragraphs of Church Dogmatics §64.2. I love the wheel/spokes piece:
To be sure, certain analogies to the relationship between God and man, God and the world, are established and made possible in His becoming and being. One such is the relationship between heaven and earth described in Gen. 1.1 and often mentioned later in both Old and New Testaments. Again, the being of man as husband and wife (Gen. 1.27) is expressly described as a picture of the living God of Israel in His action and co-existence with man and the world. The relationships of father and child, king and people, master and servant, frequently emerge in the Bible as correspondent to this relationship. Everywhere analogies have their proper place where it is a matter of consideration and understanding of the covenant as it was willed in God's eternal counsel and fulfilled in time in the incarnation of His Word. Again, in the connexion with their earthly surroundings the fulfilment of the covenant, Jesus Christ and the kingdom of heaven are all open to comparison. In this connexion they are obviously made a subject of comparison in the New Testament. But in Jesus Christ Himself - and it is of Him that we now speak - we have to do with the eternal basis and temporal fulfilment of the covenant and therefore with the ground and basis of all the natural and historical relationships in which the covenant is reflected as the basic relationship between God and man, God and the world, and in which it therefore has its analogies. We have to do with the presupposition of the connexion in which it can also be a subject of comparisons. In Him we have the basic reality which underlies the possibility of the basic relationship of the covenant, and therefore all the natural and historical relationships, and in Him the analogies, and therefore His own connexion with His earthly surroundings and the comparisons which it invites. In Him we have their beginning, their meaning and their goal, the centre which invites and carries the whole, both creation and the covenant. This centre is the divinely established unity of existence between Himself and man, the unio hypostatica in the one Jesus Christ. But as a wheel with its different spokes can have no spokes in the centre, so in this centre of creation and the covenant, the origin even of its own connexion with its earthly environment, there cannot be a relationship between God and man, God and the world, which is comparable to natural and historical relationships, having an analogy or likeness in relationships of this kind. That the Creator became a creature, the Lord a servant (and, as a servant, and the Brother of all other servants, genuinely the Lord), the divine I a human Thou, God's existence the existence of an essentially different man - in other words, the becoming and being of Jesus Christ - cannot be understood and apprehended, either in advance or afterwards, by means of any reflexion which looks beyond Him or from any neutral place apart from Him. With a strange, one-sided, self-glorious spontaneity, we have to do here with the work and action of the faithfulness and omnipotence and mercy of God Himself, which has no ground of reality except in Himself, or ground of knowledge except in His self-revelation.