SBuilder ground textures at night, plus knock-on problems

I have a problem with a "clash" between a revised grass background texture to an airfield and an adjacent (new to fs9) town texture. In daylight everything is fine, but at night the lights etc of the town texture spread into the adjacent grass texture. I then changed the "ground_VTTP.bgl" which had both textures in it into two separate bgl's, "ground1_VTTP.bgl" and "ground2_VTTP.bgl" but this gave birth to a different problem in daylight. I tried with them both in the same scenery folder, and also in separate folders with different scenery library priorities, but the result was either a complete grass background with only a partial town, or a complete town and only partial grass. The town spanned across a junction between two LOD's and with a full grass background to the airfield the only part of the town that survived was the part in the adjacent LOD. This is the second time I have had this problem and I didn't manage to come up with a solution the first time either. Ideas?