To improve the benefits of hunting in a small party, the party experience bonus obtained when killing monsters has been changed as follows:
2 member party 7% -> 30%
3 member party 14% -> 39%
4 member party 23% -> 50%
5 member party 31% -> 54%
6 member party 40% -> 58%
7 member party 50% -> 63%
8 member party 61% -> 67%

When you group together to hunt as a party, you earn less per kill (because you're sharing the EXP and SP with your group) but there is a group bonus that increases the total EXP and SP awarded.

When two characters group together to hunt, there is a 7% bonus. For each additional member there is an additional 7% bonus.

If all members are the same level, EXP and SP are shared equally. If there's a difference in levels, you gain EXP and SP based roughly on how many levels you have, compared to the other characters in your group.

So (for example), if a Level 6 and a Level 4 group together, the Level 6 will get about 60% of the rewards, and the Level 4 will get about 40%. (It's not that simple — to get the actual division, you square each level [6 x 6 = 36, and 4x4 = 16] and add them together [36 + 16 = 52]. The Level 6 character gets 36/52 of the rewards, while the Level 4 gets 16/52 of the rewards — that works out to almost a 70/30 split.) However, remember the 7% bonus for grouping that adds to both characters' rewards.