I don't want to sound simply controversial, I see no need to please me! I only want to invite people to this discussion if they want to participate in it.
I may sound harsh, understand that I only want to get to the point. I don't want the autor to justify his work, his work does that by itself.
What you do, Fixer, to solve the problem is redifining what is a "share". Instead of it being a proportion % of the available vis, you make that a fixed number of vis. You determine that number based on 1the available vis. Of course it solve it, but then you encounter the problem sharing was all about solving: not promising more vis than the covenant can afford to give.
The other problem is that a mage may be able to extract more vis than the pay he gets from a season of service. I've seen that elsewhere on this forum: for exemple, if a mage build a magical object with a lab total of 30, this mean he could (comparatively) extract 3 vim vis. And that's the basic measure of a season of work. This is interesting, but brings the problem of the limited supply of the covenant.
Either you share available vis for the magus, maybe not efficiently rewarding mages, either you give a number that is the value of a season of work, risking to see the covenants store depleted.
The answer will probably lie somehere in between.
Reading Henricus, it made me react, thinking this. You talked about "incentive to do covenantwork". The question this bring to my mind is, does payment for a season really supposed to be an incentive ?
We don't have an exact french word to traduct "covenant". We use "alliance" which I think have about the same meaning in english. A covenant is really about an alliance of some magus, it should not be forgotten. They are there for a purpose, doing something togethere.
I've seen two tendency in "Alliances": it's either a commune, may be a bit like medieval monastery: most is the possession of the covenant. The mages are together, facing problems, while having some personnal interests, but those are always linked to what is happening in/about the covenant.
The other is well portraied by Birbin again here: the covenant is more of a place where magus "stick around". The covenant is a place where individual can strive toward their goals. Problem that the covenant encounter are seen as thing slowing personnal projects: they are to be dealt with then forgotten (not always, but essentially)
The second is like our first campaign. I would like to see the first happening in our current campaign.
What problem it bring, is the legitimacy of the sharing/payment system.
In an old covenant, where the young magus (players) join in, the legitimacy is historical: it is the way it is for a long time. The fact that the old magus builded the covenant gives them the right to impose their own rules.
Another thing that could help toward the legitimacy of such a system could be that many covenant use it in the Order of Hermes. "Everybody does it" "It's how it work, pal" . Such an hypothetical system would have had time to prove itself. But Covenant does not give such background element, and we are hard pressed to find what it could be. Still, when you think of it, that one or two or three major system used in the OoH ought to exist ! We can find it.
The case of a young covenant is different: the mages decides what will be the rules "from scrap". But as I just said, they probably already know some good ideas upon which to begin a discussion on the matter. The legitimacy of the system is more fragile here, because it need to be rationnal to be accepted by the majority. We play in the Rhine Tribunal. If we ask our SG how they do thing at Triamore (where my character comes from), at Waddenzee or elsewhere, he can't really answer because nobody really knows. He say: " Oh yes, your character fully knows how it works at Triamore - not in the details, but still he has a good grasp of the system." But he cannot tell what it is. It's like making a spell, your character knows how, but no player understand what his character really do in-game when he launch a spell.
I have reservation for that tendency. A covenant need new blood to survive. A player will see the coming of a new magus as someone who will demand vis. But I'm guessing that a real magus would put more importance on continuity of the covenant he tried so hard to build and protect. Only a covenant with enough reputation would be able to get new recruits while asking them to do a lot of sacrifice to join in. There could be exeptions, but still, I think this should how it works out in the OdH, IMHO.