i'm gonna pass on giving any 4bt advice cos its hard to type out the wrist curl stuff but for smooth btb transfer, i say carries work well.
these are basically spread out circles.
easiest one imho for smooth transition to btb:
spin right poi backwards on your left hand side (arm crossed in front of your body).
as the poi passes your foot guide it across to your right hand side.
it needs to get there before it gets to the top of its circle because as it starts to swing downwards again, you are going to guide it to btb on your left hand side.
so you have spun one whole circle spread out so the poi goes:
past left foot (arm in front)
past right ear
past left foot (arm btb)
once this transition is smooth, you can use it out of any weave type motion to transition to btb or waistwrap positions in just one beat.