What 30 percent?

30 square inches is 23 percent of the 130 square inches you mention. You mention however the "total area" of 130 sq.in is the horiz-stab. I was guessing that "total area" was actually for the entire tail. But it'd be better to clear up the numbers.

What was used before in the entire horizontal tail?

But bottom line is that anything is going to work, especially around 20% for the elevator. Going smaller requires greater deflection. Going larger requires less. Less deflection should result in better efficiency. But the difference in efficiency isn't going to be much. It'll only matter on something like a glider and then not a lot.