Ok, I've made some progress - I've confirmed that the CFG folder sits in the right place, and I've confirmed that my changes are being updated. Now in MAME, a cocktail game starts in horizontal mode, and the screen flips for the second player. So far, so good, except that for the purposes of my 3-sided cocktail, I need it to start in vertical mode - not horizontal. Now to GameEx, and in Cocktail mode the screen is vertical and split - again, so far so good. But when I play the game, it goes to exactly how it is in MAME - horizontal, and flips for Player 2. What am I doing wrong here? I'm not fussed whether MAME or GameEx starts the game in Vertical mode, but one of them needs to..... Thanks again.