Bendover is quite correct (I should have investigated more)........much of this could be improved just by choosing other arena settings although there is a function of the alpha map used in bump mapping darkening the ground tiles.
The following is with bump map on and we can clearly see the rectangular aspect as the bump map is engaged with range.
Also the sky (bluer)and fog(slightly bluer) colours have been changed below as well as the light being changed from white to white with a hint of blue. I also changed the sun to white with a hint of yellow. Bump mapping is now removed.
low down this still gives a very nice aspect of land and sky and the floor tiles look brighter.
Obviously it would be nice still to enjoy bump mapping so i would hope that the "transparant" part of the Bump map alpha mask can be made truely transparant.
I think it would be neat if the fog was either able to go out further than 17 miles or its denisity/distance gradient as haze be changed to make it less obscuring on the near side of its band.
The light from the sun would benefit from the ability to adjust its brilliance as well as its colour.