The promotion zone in the Diagram is always the furthest N ranks. So if you set it to 9 on a 9x9 board it would be the entire board. If you want just your own back-rank you must use a morph for the promoting piece, with which you can define any irregular promotion zone. Like
morph=///////*
on an 8x8 board (7 ranks without promotion, one with the normal choice, counting from the furthest rank). Add this after the Pawn line of the Diagram, and then paste it back into the PTA, and generate GAME code.
[Edit] On second thought, morphing with choice might not be implemented yet in the GAME code. In that case I am not sure what is best, also because I don't know what exactly you want.
The promotion zone in the Diagram is always the furthest N ranks. So if you set it to 9 on a 9x9 board it would be the entire board. If you want just your own back-rank you must use a morph for the promoting piece, with which you can define any irregular promotion zone. Like
morph=///////*
on an 8x8 board (7 ranks without promotion, one with the normal choice, counting from the furthest rank). Add this after the Pawn line of the Diagram, and then paste it back into the PTA, and generate GAME code.
[Edit] On second thought, morphing with choice might not be implemented yet in the GAME code. In that case I am not sure what is best, also because I don't know what exactly you want.