I don't know of any strings that go high and low, but one mix up you could do I suppose, if f+4, because you can go either b+4, to do the sweep, or press 1 to do the overhead. Its not much but if they get caught up by the sweep, you could perhaps bait out a wake up attack and punish it. If they start blocking the sweep, you could do the overhead. Like I said, it isn't much, but it's a little something extra to keep people on their toes.
If your friend has started jumping you, then after the f+2,1, do a jneutral jump punch. The odds are that when they are jumping, they will not hit the attack button immediately, so you will catch them with a njp (neutral jump punch) then you can do any of your juggles. If the njp doesn't connect or they jump back, you can whiff the njp and thow out an air fan, that they will eat if they start jumping backwards.
Also as regards to hitting the U+1? You can do u+2 as well. The way that I do it, is after the f+2,1, I tap the u,~1 or 2 as the opponents character is approaching the peak of the launcher, or you can start it as Kitana is about to land from her f+2,1 (both are around the same timing). There is a technique that Wonder Chef over at Mortal Kombat United said. After the launcher you do whats called 'Pianoing' which is when you tap 'u', you immediately do 1~2. This should double the chance of the neutral jump punch coming out. I hope this helps.
Mystery, did you happen to check out the video link that I posted to Silent1s show earlier in the thread? If you follow that link sir, you will get a good breakdown of some of the tricks you can do after the f+2,1. If you can't locate it man, please send us a PM and I'll send you the link!!!
