Is Myrtle a foil for Gatsby?

There is a section of the Tyson chapter on Psychoanalytic Criticism that sparked my curiosity on this matter.  According to Tyson, “Daisy doesn’t realize it, but Gatsby and Myrtle function in much the same capacity for the Buchanans:  as psychological pawns in their relationship with each other” (46).  Both Gatsby and Myrtle serve as extramarital lovers to characters who demonstrate a “fear of intimacy” (39).  In that sense, they have similar romantic roles.  However, Myrtle differs from Gatsby in numerous key ways, which serve to accentuate Gatsby’s, well, better character.  Myrtle is the sensuous mistress, while Gatsby is the hopelessly devoted romantic.  Myrtle is low-class but trying to climb the social ladder, while Gatsby is wealthy to attract Daisy.  What are some other parallel differences?  Is this enough to say that Myrtle is a foil for Gatsby?  I know foils are usually of the same sex, but the parallel contrasts are interesting to me.  Maybe that’s all it is – a complex use of contrast?  I’m not sure.  Any thoughts?