1. Formula:

rate_exp_pvp = 2 (This one depends from world config and can be checked here)
a = attackers level * 0.9
b = victims level
c = victims experience

result = (1 - (a / b)) * 0.05 * c

result * rate_exp_pvp

2. Restrictions:

-Attacker's level comparing to victim's level cannot be higher than 30.