Really, this comic could have just been the first panel and I would have been happy.
It's been established several times that the TF gun has size change limitations. Big as Greg is, he would look significantly different to most men hit by the FV5 beam via the TF gun.
Magic users, however, are generally able to ignore such limitations, and Ellen being Ellen, I felt she should be able to. I also felt, however, that she should be able to get exactly the same result as the TF gun.
Obvious solution: Ellen can just put more power into the beam if she wants to.
And for anyone wondering, I concluded that Greg is so tall and bulky relative to either FV5 result that almost everything he's wearing would realistically just fall off. The more muscular result has hips wide enough that one might question this, but once I considered depth, I reached the conclusion that not even those hips would be enough.
Which is, of course, why they wound up wearing tank tops. I determined that, while they would appear comically large, they would at least have a chance of staying on while also keeping them covered without resorting to angelic birds or whatever.