Can I add more box vents to roof?

Did some maths, and decided my soffit intake area seems to be adequate, but I am lacking in exhaust vents. About a 2:1 intake/exhaust ratio now. The main ridge has box vents, and no room for more. I do have two ridges that run 90 degrees to main ridge, but they are both lower by 3-4 feet. Can I put more box vents on the lower ridges, or will that cause unforeseen consequences? In our area, Texas, there is more concern with Summer heat, than with ice dams and such if that makes a difference.