If the infantry et al is elsewhere, it could mean there will be nothing left in that hex given that everything could just fly off (as has been theorized elsewhere), leaving Jetstone forces defending an unimportant hex. People have already pointed out that the easiest way to deal with a concentrated opponent is to not engage them, and hit soft targets. If the only decrypted actually in that hex are Archons (themselves knight-grade), then it becomes a certainty that Wanda is elsewhere, leading the main GK force (which Jetstone has shown themselves to believe a serious enough threat to do overkill on the bridge hex). That at least would let people rest at ease that her Magenta phase won't last, if it's just an Archon with a veil to look like Wanda (who had different battle armor already drawn page 2).
Wanda should be wherever the most valuable enemy units are.
In fact, the Jetstone casters are uniquely vulnerable to capture now. If Ansom can take the hex, they won't be able to send them to the Magic Kingdom.
He may yet be planning to hit the bridge hex. The benefit of the veil could have just been to have Jetstone configure their defences assuming siege (and to move the casters out of the city). Thus, Ansom's force would be optimised for destroying them.
3 extra casters is a pretty large prize, and could be worth the risk, even if they were planning to hit the capital.
A dittomancer doubling all of GK's bonuses would be pretty devastating, especially since bonuses are one of their main advantages.