Not sure what this has to do with the MapSessionMerger. I don't mind taking a look, as Mqurius has left the H&H scene ... But your not giving me much data here to go by. (I also don't actively use Mqurius map merger ... as I don't have a need for single file merged maps.) --- Just in case: "MapSessionMerger" and "Mqurius map merger" are two completely different tools! (seems you mixed them up by the look of it.)
Having squares n the corners is aesthetically pleasing, but it means that the chain reaction for a ram can quite easily knock down segments of both walls. if you want to actually require two attacks they cant be connected...