I like how you try to catch lively attitudes in some of your sketches. May I suggest you try the same in your no-reference work? It's more difficult than standard attitudes, but it's far more interesting and motivating. When drawing so, don't hesitate to experiment a lot of slight variations until your eyes tell you it clings, and if this doesn't work, start again from scratch. I don't know if this is an efficient method, it's only my way of doing it.