"I'm not sure how this would work for someone with two dependents, who would receive $4,200 with an AGI of $75K"

You mean how the current math is used?

"For individuals with qualifying children, these total-phaseout amounts increase by $10,000 for each qualifying child. For example, for an eligible individual filing as married filing separately with 3 qualifying children, the individual’s payment is reduced to $0 if his or her AGI is $129,000 or more."

That's up from $99k.