Probability = number of events/number of likely outcomes
If the probability is already set at 1/6 you have a 16.66% chance of getting raid loot.
if you have more people the probability of getting raid loot is
2/12 =16.66%
3/36 = 16.66%
4/48 = 16.66%
5/60 = 16.66%
6/72 = 16.66%
7/84 = 16.66%
8/96 = 16.66%
9/108 = 16.66%
10/120 = 16.66%
11/132 = 16.66%
12/144 = 16.66%
So if you have 1 or 12 people in your group the chance for getting raid loot as an individual or group is 16.66%. Alternatively there is an 84% chance you will not get raid loot.
That is what this new system means.
Need I say more...