We explore the heavy-quark mass region above the charm mass using M\"obius domain-wall fermions on fine lattices at $a = 0.080$, $0.055$, and $0.044$ fm. We examine masses and decay constants using a series of heavy quark masses up to 3 times the charm quark. We analyze the cutoff effects for heavy quarks above the charm and account for the leading order discretization effects using ideas from HQET. We extrapolate to the bottom quark mass and report preliminary results for $f_{B}$ and $f_{B_s}$.