Anyway, spent some time looking at it and realised that, although they appear effortless, there are many layers of working going on in them. I had mistakenly assumed that after sketching and all the prep work, that he would lay down the colour, and then do the line work over the top. But I can now see that he builds these apparently impulsive gestures very slowly and methodically.
Take this area of Mr. Kessler and his horse.
Although it at first looks like line over blocks of colour, if you study it you can see the order in which he worked.
After first ( I assume ) sketching the image on the canvas, he laid down the base colour for the Horse (A), then working in a warmer body colour (C), and the outline in brown (B).
On top of this he drags a brush loaded with half mixed brown and white for the Stirrup leather (D), before outlining this in the brown as well (E). Then, clearly over the top of these he draws a stroke of white for the metal of the stirrup (F) before a brush of blue to colour and outline it (G). Then another layer of the brown for the boot toe (H), before finally outlining this in brown as well (I).
Seeing how these layers overlap means he took time with these apparently loose paint gestures, allowing the oil to dry between times. And even though, in themselves, each mark appears impulsive, he had planned exactly how he was going to depict each piece.
So believing I can do a sketch and then just whack some colour on it will only end in unsatisfaction. Need to look closer, and more.