First thought is radius of power, since I used gambling as an example, we will day 6 feet for the average casino table. A gun aimed at him from 6 feet or less will jam or misfire, but someone shooting at him a in a chase scene will work just fine. If we use the example of Domino, she had a mild telekinesis that she used subconsciously to move things into position to her advantage such as leaping over a trashcan would flip the lid up and block line of sight or a chipped clay pot gets hit stopping the bullet but making the ceramic explode into less damaging projectiles that scratch him up bad but not as bad as a slug in the shoulder.

The biggest and most definable is just the 12 foot bubble as his area of effect.

Also (the more I type it up, the more I like this idea) we could go with "luck absorption" of say 10% probability from each person within 6 feet of him with him having a natural 10-20 percent just sitting there. He just needs to find a spot with 10 or more people in 6 feet radius, 12 foot diamater (easy as hell in a casino) and his luck won't run out. IF we use this method, I would be more than happy to let the GM roll a 10 sided dice and decide if it succeeds or not. Biggest gaps here are obviously if he is alone in an alley, he only has himself to borrow from or anyone more than 6 feet away like a firefight.

If we use kinetic absorption, he touches a person and absorbs their luck (10%) and can only absorb until he releases. Same example above: he walks to a table, shaking hands and touching shoulders as he gets to his spot. He absorbs 10 peoples luck but can only hold the charge for a few minutes, lets say 10 minutes for this example, he walks into the casino,touches 8-9 people walking up to the craps table, places his seven bets and burns his luck. He wins the 770 and walks away and cant absorb luck again for say an hour. An hour is long enough apart for him to rest, have a drink, watch the 2:30 band set and then touch ten new people on his way to the high roller table.

We can put some simple limits on this: He can't kinetically absorb from anyone thicker than regular clothing so even the kevlar suits casino security and millionaires wear would require skin-to skin. He can't kinetically absorb from people who know to be on guard, like gambit's charm ability only works on those unaware he can use his charm ability. The time charge where he has to use it in ten minutes and cant use it again for an hour. He can only use it in bursts, not partitioning it out.