After naming your fixture, you are asked to configure the type of fixture.
If you configure it as a dimmable light, you will be asked to set the minimum dim level (the point at which the flickering will stop).
Set the low end of the dimming range by starting high, and dragging down on the slider to control the brightness of the light. When the light starts to flicker, bring the slider up until it stops flickering.
This will set the low end of your dimming range, so that your lights don't flicker when you dim them.