Flower sweep is possible, but difficult if you keep good posture and control over their hips. They won't have great leverage over your body given the distance, and since you're pressing so hard into their hips you will slow their hip movement down (or at least know when they're thinking about attempting the sweep). Assuming you are both similar size, you should have a good chance of keeping your balance and avoiding the sweep. Also, standing on both legs will give you quick mobility (it's more difficult to flower sweep a standing opponent, even if their posture if broken). Finally, if they are trying to execute a flower sweep, similar to the omoplata they will need to open their legs, and that will give you an easy triangle escape if they don't break your posture and free their hips first. Similarly, in this video, the omoplata attempt is only possible when the guard player frees his hips by manipulating the top person's, and the attack will probably not succeed ifMarcelo maintains his posture as he does in Technique 2 and 3.