Oh, America, what have you done.
Ah, I see. The BRASS dragon's melee value will still be 4; its ability does not become inactive when it's not on top.
I play this dragon on top of a metallic dragon, which increases both of their melee to 4.
(The metallic dragon underneath the Brass dragon doesn't have its melee value increase to 4 unless it too is a BRASS metallic dragon, by the way.)