Yaz, maybe you can bend your knees and ankles more? Ankle bend is very important. Your ankle should be pressed against the tongue of your boot. Even though you're bending the ankle, you must still glide on the back of your blade. Don't lean forward. If you do, the toe-pick (or even the rocker) will act like a brake and slow you way down.
Another thing to check is to see if you have a break on your waist. When I first learned my back outside edge, I was so afraid of the lean. I over-compensate my fear by breaking at the waist and of course the result was not pretty. Not only it looks ugly, it also slows me down.
The best exercise for me to learn back outside edge? Hours and hours of crossovers. After months of crossovers, my legs become much stronger and they can bend and "HOLD". The key here is "HOLD". The longer I can hold on each edge, the better it looks (and it also glides much faster!)
Concentrigal force does play a trick here. The faster I skate, the easier for me to have deep knee bend and good lean.
Hope this helps.
