But the incentive to fly should not be money. Don't get airborne 'to log hours' simply because you need the money. You are there for the student and I would suggest only flying if the weather is going to be favourable for the lesson and to give the student the best opportunity to understand what you are teaching.
I would ask for a retainer as well because, lets be honest, the weather can be unpredictable at the best of times.
I appreciate you are a restricted FI but the moment you have your restriction lifted, ask for more.