Mastery Abilities and Ritual Magic

I can imagine that there are topics with thats questions...
How does the Ritual Magic work with the Mastery Abilities Fast Casting and/or Multiple Casting?
I can see taht the first is a impossibl but i have doubts about the second, please answers with your opinions, thanks.

I doubt it's possible: casting two formulaic is easy, but casting two rituals (or more!) at the same time would require: handle 2x (or more) the vis, in the limit of tefo pawns... besides the risk, the concentration required (15 for each one, by 15 minutes...).
It would be statistically, always a botch on concentration, thus a waste of vis, and one would say that could even lead to a test for botch in casting, hence a possible twilight.

I don't see why multi-casting would require Concentration. That was pretty much discussed before.

I think it comes to: can your troupe come up with a reasonable way to allow ritual multi-casting and be happy with the result?

I'd want the stalwart (no fatigue), imperturbable (concentration) and boosted (spend vis to improve effect) masteries first for pretty much any ritual.

Thanks for your responses, Multicasting rituals have risks yes, but if it's possible then if First doesn't take any longer because the rule, but still costing Vis (I was sure about that) with the other limits, then it's power breacking, only grant a little less time on Ritual Magic.
If any opinion is on the air, please writte it, thanks.

If each application requires its own vis and its own fatigue, multicasting is weaker than Stalwart. Which makes it okay I guess.