As far as I'm aware, it was the intent that the Power property of the Magic Book item class, would determine the damage of flames created with the wand; however it seems that this is not happening. Was this function never implemented?
[2.50.x] Setting Power of 'Magic Book' Does Not Affect Fire Damage
Yeah, I first discovered this when I tried to make the book more powerful in Zelda 3, didn't work 😞
The book's power determines the strength of the magic, but the fire's damage is fixed at 1. I don't see any evidence either way as to whether that was the intention. It certainly would make sense to add, in any case.