All of you have already seen you never give really the % u thought give to the guild.
Let me explain you how XP given to the guild works.
1 - %XP given to the guild is XP you lose from a fight
XP you give to the guild is fully removed from your experience.
That means if you should win 10.000 xp, if you give 50% xp to the guild, you'll win 5.000 xp only.
2 - XP given to the guild is divided
But, on these 5.000 xp, guild doesn't win 5.000 xp.
There is an arithmetic made.
First, for everybody, this xp is divided by 10, so you can give maximum 500 xp to the guild.
3 - XP given to the guild depends your level and your guild level
Then, the game see the difference between your level and your guild level. The bigger the difference is, the more divided the xp is.
If your level is almost equal to your guild level, you'll give 500 xp (the maximul you can give). If your level is farther, then the game will remove some more % xp you give.
In the worst case (that means there is more than 70 level between you and your guild), you'll give minimum 10% of the xp you should give. That means you give 50 xp in this case.
4 - To rezumate :
A fight at 10.000 xp, a guild level 30 and 50% xp given to the guild :
A player level 30 will give 500 xp (but he'll lose 5.000 xp).
A player level 100 will give 50 xp (but he'll lose 5.000 xp too)
But we must notice that a level 30 who wins 10.000 xp is like a level 100 who wins 100.000 xp, so all members give as mush as other members. But the level 100 will sacrifice more xp (10 times as xp).
Informations given by a developper