Regardless of the specifics, the distribution of tips has been developed by those involved in order to fairly reward those providing service.
No need to reinvent the wheel. If you tip the recommended amount, it will be fair.
We always prepay and then add at the end of the cruise.
I have also started giving random tips to those who likely never get one-the washy washy person at the WJ, a guy painting, etc. It really makes their day. I simply keep some ones in my pocket and give them out spontaneously.
Happy Sails to You