There were a lot of things that went into a proper upper block. The arm was punched up, not raised, which delivered more power. The palm side was snapped forward at the perfect instant to drive the ulna as an attack into uke's arm. A bad angle made a bruising contest of power, the perfect angle could glide a baseball bat without bruising. Minimal bruising, anyway. A good snap could open up his whole centerline.
Then, one day when I was bored or tired or something, I did it wrong. In line drills I blocked the big right downward hammer fist with a right jodan uke, cross body. Most of the same stuff happened except it turned uke's entire body, made him lean slightly and I was on his flank, halfway behind him. I owned him. Playing around, it was even better when I didn't step back. Closed the distance. Hmmmm.
Chi sao, or sticky hands, is primarily a sensitivity drill. You face your opponents, wrists touching, and try to tag each other (I have a gift for oversimplification). The cool thing is that if you can maintain wrist contact you can tell not only what your opponent is doing but what he is about to do. Without turning it into a strength contest, you can 'steer' his attacks to safe zones.
Just for fun, next time you play chi sao, take a half step forward and apply the skills to his elbows. Not only can you control his attacks, you can control his entire body like he was a rag doll. If you don't piss away the principles you can even bend and fold someone much bigger and stronger. Don't take my word for it. Try it.
Lastly, referring back to an old post.
There are a lot of connected principles here. It is easier to steer a moving object than it is to stop one and the threat in a fight tends to be a moving object. Maximize your leverage and utilize structure- and know, in a body, specifically where the leverage points are. Get to a dead space (love that rear flank) or force the threat to present it to you. Learn how much you can control without even using your fingers. The whole body is connected, if you can control the threat's elbow, you can control his feet (when I use the phrase 'core fighting' I'm talking about using the connection through the spine and hip and shoulder girdles to influence or control part of the threat's body by another part. It's fun.) Lots of things work better at closer ranges than they are commonly taught.
Something to think about.