I tried a wide front lever on a bar today... and it completely changed the difficulty. It was way harder! I can easily straddle it for 20+ seconds, but this widening made me stick to adv. tuck. Plus my shoulder was getting cramped. I can see it would be harder on rings because you can't really push the rings out for it, but it definitely works on a bar.
I don't know why I didn't think of this earlier, it's a great exercise.