20.8Bass + melody narrows the chord dramatically

Suppose you're in C major.

Bass note is F.

Melody note is A.

Possible obvious chord:

F major = F A C

If bass is D and melody is F:

likely:

Dm = D F A

If bass G and melody F:

likely:

G7 = G B D F

So hearing just top and bottom voices gives a lot of information.