yes it will be like that rob,but keep going as it will be well worth it in the end.no matter what you do to it though the fuel consumption will never be great,just live with it mate.also consider fitting a psi power box to it,i fitted one to mine and it made a big improvement to the power and a little better to the MPG.
If fitting a "PSI" box or similar keep checking your m.p.g.figures without using the on-board computer. The box "fires" extra fuel into the system "dowmstream" of the computer so it`s not aware of fuel being used. Would agree wih you it`s best to sort out any under-lying problems before fitting any mods as they could hide faults. Your fuel use doesn`t sound excessive to me, but following he advice from Wammers etc should make sure the engine`s running sweet.