Excessive gem usage in combat?

[LintMan]

Wierd, in my current game, I supplied Luigi the Witch Hunter (2F 1S 2H) with 10 Fire gems, something I hadn't really experimented with before. And I'm really confused now about what happened...

I scripted him to cast Phoenix Power, Flaming Arrows, Incinerate, Incinerate, Incinerate. Those are all 0 gem spells except Flaming Arrows is 1 gem.

I sent him into battle, and because he gets my pretender's water 9 quickness blessing for sacred units, he gets quickness and the script is mostly thrown out the window.

Anyway, at the end of the relatively short battle, I check up on him and discover 9 fire gems were used, despite him only casting 3 rounds of spells!

I just went and reviewed the battle, and watched what he cast, and how many gems were used for each casting:
Round 1:
-- Phoenix Power - 0 gems, so far so good
Round 2: (now blessed, so he's casting 2x spells per round)
-- Flaming Arrows - 3 gems! Since Phoenix Power boosted him to 3F, shouldn't this just cost 1F?
-- Fire Fend - 3 Gems! This should also only cost 1F.
Round 3: Summon Fire Elemental - 3 gems. This is only a 2 gem spell

At this point, his fatigue was something like 162, and he's done for the battle, having cast 3 spells costing 9 gems total.

I suspect that those extra gems were somehow used to raise his level even higher to lower the fatigue cost, but I don't quite understand how that works. I had thought extra gems would be used to get a mage up to the level to be able to cast a spell, not beyond that.

Is there any way to control this excessive gem usage? I gave him 10 gems thinking it'd Last him 10 game turns/battles without needing to resupply from a lab, but he burned 90% of his gems in one battle! I can't afford to spend 9+ fire gems per fire mage per battle! And mages can only carry 30 gems - do I need to bring him back to a lab to resupply every 3 turns?

Yikes!

[PvK]

No, they also can use gems just to cut fatigue costs. Often seems pretty wasteful, especially if you were hoping the gem stash would Last multiple battles. So sometimes it is a good idea to have non-casters (hiding scouts are a good choice) carry a gem supply, and only hand out gems that you don't mind them using in the immediate battle.

PvK

[Norfleet]

If you give a caster gems, on most spells cast, he will use gems up to his caster level to reduce fatigue. Since with Phoenix Power, your mage is an F3 mage, he can use 3 gems per cast, so will cast the spell using 3 gems nearly every time.

[LintMan]

Ahh, OK. That all makes sense, I suppose. I also hadn't realized that scouts could carry extra gems.

Thanks for the info!