Ferndale,
The reason for the slanty side down is that you only need to retain the driveshaft at the bearing's inner race. The outside diameter of the collar is such that if it were used with the slanty side up, the flat face would interfere with the stationary outer race of the top bearing.
Just ordered a few Microheli goodies for HBK....new main drive gear, main blade grips and parts which will upgrade the head to metal balls for the links.
Guitarist coming in a minute but just thought I'd check back to see what's going on.
Ray