Michelle Heer wrote:
...How is the roll from standing different from the roll from being thrown?
Uke does not start with the same degree of control when being thrown by a partner. This is why I suggest that, as uke, you tell your partner to slow down "just before the roll" or something like that.
I'd tell my partner, "I'm working on my rolls, so can you stop the technique just before you throw me until I get the feel for it on this throw?"
I believe the primary goal of learning ukemi is to learn to protect myself.