Its hand held (loosely) flat. No need to stretch the fingers backwards or anything. For me, its about 1 1/2 tsp or 1/2 Tblsp. A heavy palm has fingers slightly curled, around 2 or 2 1/2 tsp, a bit shy 1 Tblsp. You are only looking at the pocket formed in the middle, not the whole "hand" less fingers and thumb. /edit that's a "flat" measure, not a pile. With piles, you can easily find 1/2 cup and 1 cup with the right hand position.
That's enough salt to extract the right flavors from the bone, but not so much it becomes very salty when cooking it down. Always have to add more later, when I finalize the dish - but you can always add, taking away is far more difficult. And since many starches need to be cooked in seasoned (salted) water - potatoes most notably - not being able to add more is a direction I try to avoid.
Take some sugar and some measuring spoons, you'd be surprised how useful your hand is for measuring things (except baking, that's chemistry!)