Kneeling is probably the most unstable shooting position next to standing. When I went through one of the military’s sniper courses, we only practiced kneeling at 50-75 yards and our target was 12 inches in diameter.
So as for some feedback on your picture of kneeling, it looks very unstable to me. It also looks like you expose a lot of your vitals in that position, namely your femoral artery. If you back away from your barricade, you can expose less of your body and vital areas. We had a saying during CQB building clearing, the only cover you have is the end of your barrel.
When it comes to kneeling, I prefer tucking my foot under my butt and my other leg bent in a 90ish degree angle, then resting the back of my bicep of my support arm on front of my raised knee. This is muscle to bone and not bone to bone. If you go elbow to knee cap it is highly unstable, like two ball bearings on each other. This position is very low to the ground, almost like sitting. I did make a hybrid position similar to this with the change being resting the rifle fore end in the crook of my elbow and reaching back with left hand and holding the sling to raise and lower the sights.
Also how far are you shooting? As a general rule I would say kneeling should be employed for targets from 25-50 yards with the exception of maybe during a fire fight were you have to take cover and are being pinned down.