Different offices, different requirements. Present what is asked for at IO you use.
You will get alsorts of different answers on here due to personal experiences. The differences between IO's should not exist, but it does. Its down to individual understanding of the rules. I'm sorry to sound a but negative, but that's the way it is with any government dept. over here. Sometimes it's like nailing jelly to a wall.
If you've got the money in the bank and the required seasoning of that money then do it yourself bud. It's not a hassle and will save you the cost of an agent.