I find the key is a brief period of injection where the tip is just about surface level and produces the distinct ‘ch-ch-ch’ sound followed by plunging the tip and vortexing the milk/foam mixture as much as possible to keep it mixed well.
A few tricks that might help
-Remove the plastic ‘froth aider’ and expose the metal tip of your wand.
-Begin frothing just before the boiler reaches temp, essentially tricking the heat element to keep it on as long as possible. This is really helpful on wimpy machines that run out of steam power quickly.
I keep my frothing pitchers in the freezer. I use 2% fat milk. I do the first frothing before making the espresso; I keep the tip just under the surface of the milk, until it’s mostly foam. Then it sits and hardens while i’m making the espresso. The just before combining the espresso and foamed milk, I re-heat the foam with the tip about halfway into it. Them I pour the espresso into the cappucino or latte cup and spoon the foam over it. That make them the way I like them.