your bitcoin wallet doesn't receive the fee! it is received by miners and the bitcoin network determines how much it is based on the number of transactions that are in the memory pool and the amount of fee per weight they are paying.

don't get confused about fees that a centralized service charges you with the bitcoin transaction fees. for instance your freebitco.in account takes a slightly smaller fee compared to a transaction's fee because they are paying a lot of users at once in one transaction which would decrease the size by a little bit so it decreases the total fee they have to pay compared to if they created individual transactions for each user. and it goes up like anything else because it still has to broadcast those transactions to the network so it has to increase the fee as the number of transactions and their fee grow.