Sometimes my writing process is as simple as following logic to its natural conclusion.

"They have to picture their change in size and the change in their clothing's size separately! Wait, that could be dangerous. What if they picture the clothing too small? Well, the magic should be able to detect if it's encountering resistance, which means Tedd should be able to set a minimum looseness level, thereby making it impossible for the results to be too constricting.

Wait, if imagining the clothing too small for the resulting size change forces the clothing to default to a fit that's at worst a little snug, isn't that a guaranteed method of avoiding wardrobe malfunction with the watches?"

Yes, that's right. Logic is applicable even in the land of EGS. Just don't tell anybody.