I was thinking about the eventuality of an exp buff, and I would like to give my advice to GMs in case its coming so I was computing on excel and I think the following formula would be something plausible.

Consider the parameter belows:

MAX=Max Level of Grouped Players
MIN=Min Level of Grouped Players
#=# of players grouped
Tot=Total level of Grouped Players
X= Metric to be chosen (for solo)
Y= Metric to be chosen (for grouped)
Z= Metric to be chosen (for bonus per group member)
A= Metric to be chosen (level disparity for PL)

The formula would be:

ExpBonus=IF(MAX>A*MIN,MIN/X,IF(#=1,Tot/X,ToT/(#*Y)+#*Z))

This means that if the max level of the grouped player is above "A" times the minimum level of the grouped players, where A is to be chosen, then the exp bonus is the same as if the low level player would be playing solo (for all grouped players).
If it is not the case, meaning all players are within the Minimum player level * A then the exp bonus is calculated as follows:

Total level of all players in the group divided by the number of players in the group, which is multiplied by a metric to be chosen [this serves the purpose of tuning the exp bonus to a level appropriate to Uthgard 2.0] . To this is then added a group bonus that is the number of grouped players times Z where Z is also to be evaluated by Uthgard staff.

Regardless, if playing solo the bonus is Player Level/X where X is to be chosen by Uthgard staff.

I personally took the freedom to put some values for A,X,Y,Z:
A=1.5 meaning the level range should be withing 150% of the minimum level of grouped players or the exp would be considered solo exp.

X= 1.5 Which means that the solo bonus exp is equivalent to 2/3 of the player level or 13.33% for a level 20 player.

Y=2 Which means that the average level of all grouped players is halved to calculate the base grouped exp bonus.

Z= 1.5 Which means that for each additional player in the group the exp bonus is increased by 1.5%

If I compute the data, with my chosen metrics with multiple scenarios, this is what I obtain:

Scenario 1: {20} 13.33% exp
Scenario 2: {20,50} 13.33% exp SOLO EXP
Scenario 3: {20,20} 13% exp
Scenario 4: {20,20,20,20} 16% exp
Scenario 5: {20,20,20,20,20,20,20,20} 22% exp
Scenario 6: {38,40,44,46,47,48} 30.92% exp
Scenario 7: {40,41,42,42,46,46,49,49} 34.19% exp
Scenario 8: {48,48,49,50,50} 32.10% exp
Scenario 9: {49, 49, 48, 47, 32} 21.33% SOLO EXP
Scenario 10: {49} 32.67% exp
Scenario 11: {2,2} 5.50% exp

To conclude it means that PL exp will receive a buff, but the buff is the same as the solo exp buff; Grouped exp will receive a buff that increases together with the level of the players; the more people in the group will generally mean increased exp by a small amount; the exp bonus is situated between 0% and 37%

I would keep A between 1.3 and 1.7
I would keep X between 1.5 and 1
I would keep Y between 2 and 3
I would keep Z between 1 and 5