Completely agree on sport band or canvas and one notch tighter and higher up from the wrist "bump". Also helps when lifting weights by being out of the way on serious bending of the wrists.Reading your several posts on this thread, it seems you've given up on the watch as far as fitness/HR tracking goes. I know its a bit much to be told to buy something else to make your $1k+ watch work, but I really can't recommend the sport band strongly enough.
I have a link bracelet that I wear daily, however I swap it out for a sport band every time I go and work out/run/bike. I do this because the watch really is better at reading your pulse when tight around your arm... tighter than I'm comfortable adjusting my link bracelet (worried the stress from arm expansion/contraction could bust a connection along the band). As someone else said further up, the heartrate reading is much more consistent/accurate when you attach the watch about 1-1.5 inches above where you typically wear a watch (I attach mine about 1" above the bump on my wrist from the ulnar bone). Attaching it this high up means you need to tighten the watch fairly tight because it will just slip down your arm as soon as you get sweaty... which is why the sport band is really almost a 'necessity' for tracking workouts with the apple watch.
Last week it was so muggy the sport band was starting to slide so I purchased a cheap canvas band to try and after one try it was even better at not sliding.