Re: Keep your hands in front of your center?
I have to say it:
The M18A1 Claymore mine has printed in BOLD letters:
"FRONT TOWARD ENEMY"
Front is where the attack comes from, whatever way you happen to be facing at the time.
This is why, as I see it, koshinage and ushiro waza are hard for beginners to get. They do not immediately understand that subtle projection of energy (vector of force, as you choose) toward the opponents center that makes the techniques work.
Just as with the claymore mine the projection of energy had better be in the direction of uke's center. Even if he is behind you.