I do the technical stand up sweep from x-guard a lot. sometimes when it's not working I try to pass the guy's leg over my head and take the back with the babybolo-style hooks.
But mostly what ends up happening is that I am just giving the guy side control. I pass the leg and he sliiiiiiides right into a dominant position.
What gives? Any tips? Thanks
Gotta grab the belt or back of the pants on that one bro 
There is a sleeve grip that prevents this. It's in Marcelo's book I believe.
I had that book but my dog peed on it. True story
X guard is not really a back taking position. De la riva is a much better option if that's your goal. IMO.
All above grips will help. The other thing to remember is that when you pass your opponent's leg over your body, don't just immediately collapse your x-structure and let the guy get his balance back, this is what allows him to step over you.
Even with the leg over you still have to maintain control and threaten with the sweep in order to keep your opponent off balance, then transition at the appropriate time.
My best description....
X-guard set up on my left shoulder/ear.
1. right hand grips his right sleeve with a normal hook grip.
2. Use my left hand (and my body to duck under) to get his right leg on the other side.
3. Pull the sleeve through his legs a bit so I can cross my own forearm across his calf.
(this prevents him from turning and sliding to side control)
4. reach up with my left hand to grab the belt and move to the shins behind his knees.
5. without releasing the sleeve, pull him down on my shins to start the back take.
6. set your left hook first.
7. release the sleeve just before you set your right hook.
Jeremy Arel filmed a great tutorial showing all of the details mentioned above. Here's the link. https://www.youtube.com/watch?v=AiuaXJCov8o
thanks all!
I prefer just passing the leg across to reverse X and sweeping into the leg drag instead.
Shem can you elaborate?
Pass the leg over your head for an X-guard with the opponent's near leg on the other side of your body. Then sweep him either straight backwards or overhead, depending on where he has his weight. (If he leans hard forward, you go to the crab ride instead.) Since the leg is across your body, you sweep right into a leg drag or cross footlock.
It's like any transition, your move has to be better than his. You gotta control him, otherwise his pass will beat your transition, as he has weight and momentum on his side. This is why the guys above are talking grips. I would say the belt grip is a good one to start with as its easy to get. Pull him tight towards you and use your shins in the backs of his knees to push forward and take his base away. If you do it right that should put him on his arse and give you his back.
Personally i prefer sweeps from X - there are so many.