To complicate matters further...
Even if it sounds OK at the rehearsal, it's all going to change on the night of the gig itself. Fish batter is a notorious acoustic sponge - it'll soak up all the reflections, which will have its pros and cons. You might lose the slapjack / timing issues mentioned earlier, at the expense of being to hear the other half of the band.
Is it too late to suggest a change to pie & chips instead? That might mitigate the problem somewhat.