Catalyzes the 3'- or 5'-O-methylation of partially methylated flavonols, but does not accept quercetin or caffeate as substrates for methylation. 3',5-dihydroxy-3,4',7-trimethoxyflavone + S-adenosyl-L-methionine = 5-hydroxy-3,7,3',4'-tetramethoxyflavone + H(+) + S-adenosyl-L-homocysteine Inhibited by nickel (NiCl(2) and NiSO(4)) and para-chloromercuribenzoate. Flavonoid metabolism. Homodimer. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family.