Question Essence transfers/trading within the school.

As your Will / mental discipline grows, you can make your Well have more 'gravity' to it... which results in it pulling in Essence more quickly (this is the effect that Wiz mutants have naturally as a result of their mutations ... but it does happen to a much lesser degree as a result of training/experience... though not enough that you'd jump ranks... not unlike exercise/physical training as it applies to Exemplar). More commonly, as Will improves, the Well acts less like a sieve and more like a solid container. What goes in, stays in... and is less likely to splash out as it fills up... or accidentally boil off as a result of sloppy intentions (the unintentional wish effect). The combination of these things makes it appear like you are growing the amount of Essence you can hold (growing your mana pool)... but mostly, that's a misconception. The Mage can usually acquire far more Essence in their Well than they do... they simply don't have the Will to hold it there. And most mortal Mages won't live long enough for their Will to completely contain their Well.

Those who do... and those Mages who are immortal... might actually reach the actual capacity of their Well. But by that point, they will also have likely mastered enough 'manipulation' of Essence techniques that they are no longer limited to working with the Essence that is only in their Well. As it should be. Since the only real benefits to the Well are the ability of passively gaining Essence... and 'filtering' raw Essence into something safe to use in simple spellcrafting (ie in spells that don't have Essence typing/filtration/purification as part of the spell's complexity... something that takes more spell crafting skill than an inexperienced Mage is capable of). A Master Mage will have numerous techniques for storing, refining, and manipulating Essence outside themself... and will likely only use the Essence within their Well as a last ditch effort. Especially non-mutant Mages whose Well accumulates slowly through passive means. The 'long game' of growing a storehouse of Essence would likely involve drawing out a small portion of one's Essence regularly... say, every other week... to keep from reaching capacity. This small amount would then be invested into projects to draw more Essence or exchange it for harder to acquire types and those gains reinvested until such projects grow in complexity enough to risk losing the gains... and putting those amounts into storage for other purposes.