I am skeptical of the centrifical force and heat moving the grease into the bearings theory. For the past 45 years I have packed bearings the way my father showed me (He farmed until he 35)
Hand pack the bearings, then smear a coating over the spindle and inside the hub. Not a lot, just a coating This is to prevent rust if moisture finds it's way inside. What I have noticed is that at the next service, that grease is pretty much where I put it last time. It is not evenly distributed the way it would be if this "theory" was fact.
And I am in Phoenix AZ where it gets pretty hot... Just not hot enough for my grease to flow. Maybe I just don't drive fast enough for centrifical force to work either,:R