For people who want to delegate I suggest a variable reward:
Example:
Free Delegation: he can undelegate anytime (the actual system) :X % reward amount
3 month Lock delegation: he can't undelegate before 3 month : XX% reward amount
6 month Lock delegate : he can't undelegate before month : XXX % reward amount
1 year Lock delegation : he can't undelegate before a year : XXXX % reward amount
Cordially