you should create a debug text:
Create a layer on top for GUI with a parallax of 0% x 0%, place a text object there and at the end of your events put
system>every 0.1 second condition
and action
of set text with the text object
Set the text to something like "VelocityX: " & ball.physics.xvelocity & newline & "VelocityY: " ball.physics.yvelocity
This will allow you to see exactly what cutoff point you want to force the object to sleep because you only want to take away a settling bounce, which should have a different velocity level of any kind of bump from moving along regularly.
Eliminate anti-settle when torque:
Since you are moving using torque you might want to add that to your debug info list because you won't be trying to force a settle if the ball is still rotating.
Slow motion for debug if needed:
do a start of layout events set time scale if needed to put the project into slow motion. Then with our anti-settling events disabled (D in editor while highlighted) try letting the ball settle in slow motion and picking the degree at which you want to cut it off at to still allow regular bumps from movement.
Isolate Y Velocity:
A suggestion is that you are really fighting gravity here so no point in really taking into consideration X Velocity so you might want to single out Y velocity for this one.