If your opponent stays tight and does not allow you to pass your leg over the head, keep them as tight as possible and get as much of an angle as you possibly can (completely perpendicular to your opponent preferably). Reach under the far side leg (opposite leg of the side you were attacking), which will provide leverage for the sweep. At the same time, lift up your hooked arm and swing your free leg out in a pendulum motion. Pull up on the leg you are anchored to lift your opponent and hit the flower sweep. Often you will be able to fall into an Armbar position which you can finish. If your opponent posts with his free hand, finish the armbar from the bottom as they have no defense for it from such a disadvantageous position.