It is so hard to tell how effective a pin is by a picture or video. Uke would be the best judge. Weight application is the key to osaekomi waza and that is almost impossible to determine by a picture.

I like to use the analogy that the tatami is one piece of wood, uke another, and tori is the fastener. Tori can apply weight like nail (straight down) or like a wood screw (properly torqued at an about 45 degree pitch). It's the mulitplier effect when you can increase your effective hold down weight by about 20 to 30 %. This is the key to effective pins and something that Yamashita was so good at. I know, I have been pinned by his yoko shiho gatame.