I'm analyzing the first movement of "Suite del Plata Nº1" by Máximo Diego Pujol called "Preludio" that it's on D minor, I have encountered the following progression i-VImaj7-V7, I'm not sure what is the role/function of the VImaj7, it has the feeling of a tritonal substitute but lacks the tritone, following Tarchini's Chord function chart we have that the VI as it's coming from a tonic-function chord and it's going to a dominant-function chord it serves the role of a subdominant.
So, my question is the following: Is the VImaj7 replacing or doing the role of a subdominant or it's doing another function that I'm not aware?