The coalesce is limited by the rate of separation which derives from gravity, density difference, viscosity and surface tension. If woven wire is used in the bed the thickness of wire and density of the weave are limitations.
In some systems of woven wire, the shine must be removed from the wire to achieve efficient separation. A simple test can predict this. If a drop of feed liquid falls on the weave and bounces off, the separation will not be effective. Degreasing may help. Efficiency improves with age as the surfaces become rough on a small scale.
When fiber glass works better than metal wire of the same diameter, oxidizing the wire surface should improve function of the metal wire.