Prologue: I'm looking for my father's birth family

I recently matched at 23&Me a 20 year old as a 2nd cousin . He does not match my mom, so he has to be a paternal relationship. I've been building out his family tree trying to find a candidate for my father's father. This match is a generation younger than me (I'm 50).

I also match either his grandmother or great aunt here at Ancestry as a 5th-8th Cousin (this tree shows my 23&Me match's great grandfather as her father).

According to a chart whose veracity I have not vetted, the possible common ancestors at 2nd cousin would be:

his 2GGP and my GP
-or- ­
My GGP and his GGP.

In either of these scenarios, shouldn't I match his grandmother more closely *if* our closest relationship was through her paternal line?

Should I eliminate this line as a candidate for our MRCA and assume that we are related along additional lines? In what scenario would I match the grandson more closely than the grandmother or great aunt?

I am in the process of contacting the match to see if she is willing to do GedMatch. The young man is on GedMatch, so I hope to have a clearer picture soon.