I don't know (or don't remember) where the main forum for Heroes is. I'll write it here so I don't forget.
Initially, by analogy with the storytellers, the mage's shot was added to the F key – and precisely to avoid misclicks, it was moved to the next button for everyone. And G is the only one that makes sense, as it stands for "ground."
In theory, there shouldn't be frequent misclicks, and this is the first such complaint so far.