There are several options open to exegetes when grappling with the real presence or absence of Christ in the OT:
A) Christ was ontologically present (ruling, leading, saving, speaking to his people) but cognitively absent.
In other words he ruled, lead, saved and spoke to his people, but was The Jesus They Never Knew, as he was never revealed to them, or never revealed himself, as their Saviour-King. The self-revealing of distinct persons of the Godhead being a matter that omitted from the revelation granted to the OT saints (although many exegetes would allow for puzzling, cryptic hints at plurality. Therefore he was not personally addressed by his people in their prayers, was never the object of their worship, obedience, trust etc.
The tension between presence and absence can be explained from a variety of theological perspectives on a spectrum extending from liberal to conservative. More on this in later posts.
B) Christ was ontologically and cognitively present to his people.
Pre-Augustine it was common to understand OT theophanies as the appearance of the Son of God to his people (a point made by H. P. Liddon in the Bampton Lectures on The Divinity of our Lord, 1866).
Manlio Simonetti underlines this in two footnotes in his Biblical Interpretation in the Early Church:
Following a tradition going back to the 2nd Century, Eusebius takes the Logos, the Son of God, as the object of these [appearances of God to the patriarchs and Moses], rather than God the Father. (n. 3, p. 83)
Theophilus' one concern is to make it clear that the one who walked in Paradise and spoke with Adam, was not God the Father, but his Son, the Logos, the subject of all the Old Testament theophanies. (n. 20, p.33)That the early church fathers understood the texts in this way is clear, why they read them in this way is another matter, and why many contemporary conservative evangelical scholars are averse to interpreting the texts in the same way is an intriguing question to pose.