Question about ABY OTs for boolean multiplication triples

[dnat112]

I am trying to understand some properties of ABY for GMW boolean sharing. My understanding is that ABY uses OT to generate multiplication triples for AND gates evaluated with boolean sharing, and that this OT is logically a 1-out-of-4 OT (per AND gate). I think ABY implements the 1-out-of-4 OT as two 1-out-of-2 R-OTs and instantiates the 1-out-of-2 R-OTs symmetrically such that P1 is a sender for one of them and the receiver for the other.

Is my understanding of the above correct? If so, is there any specific reason why it is set up that way? Can it also be setup such that P1 is the sender for both, for example?