I believe it goes to 400% because you haven't edited client side. You could try something like that:
// Calculate the difference of level between this attacker and the L2Attackable.
final int levelDiff = attacker.getLevel() - getLevel();
final int[] expSp = calculateExpAndSp(levelDiff, damage, totalDamage);
long exp = expSp[0];
int sp = expSp[1];
+ if(attacker.getLevel() == 79)
+ exp /= 4;
if (isChampion())
{
exp *= Config.CHAMPION_REWARDS;
sp *= Config.CHAMPION_REWARDS;
}
exp *= 1 - penalty;
L2Attackable.java line ~595,aCis.