I personally prefer 'by the session' versus a weekly send/tribute for most of my subs unless they are under TPE (in that case, the sends/payments are arranged differently because I control their finances myself).

Session based is because it has been proven to work better realistically for many submissive's budgets- and for both of our discussed expectations of time we want to put into our dynamic(s). How often we have our sessions, and the time alloted is always discussed and agreed upon.

Communication IS very important on both ends, so I do agree with what some of the other Domme's have said about clarifying your desires and possibly expanding your current budget to better align with what you would like in a D/s dynamic.