I've just found out that there is a difference between practices among various Orthodox jurisdictions in this case. I mean, in Serbia, Romania, Greece, Antiochia etc. during the Nativity Liturgy the hymn "I behold a strange and wonderful mystery" is chanted in the place of "It is Truly meet". However, in Poland and Russia the refrain "Magnify, O my soul, her who is more honorable and more exalted in glory than the heavenly hosts" is the same, but there is chanted the hirmos of the second Nativity Canon "Today the Virgin bears the Master within the cave..."
Another interesting fact is that Ukrainian Greek Catholics use the let's say, "Southern" variant ("I behold...")
Any explanation for this?