Hey bull,
Get the magnum umbrella. Size does matter! LOL!
The small one helps but lets it run off and down your shins if you are in a treestand and can't "ball up" under it. I am just over 6'2 and 235 pounds so It is tough to get under the standard size.

Other than that they are a big help. I also open mine up in front of me as a turkey blind when calling in longbeards.

SF