It's commonly said as 1/2 or 1/3. I've seen both of them thrown out there but not much else. I'm assuming the did tests to come to that approx value. All suspensions have some nonlinear component they add to output but it's generally not audible if it's a good surround. At low excursion levels it is exta cone area though. Main takeaway herr is correct.. a bigger surround doesn't generally do much either way for cone area but can help xmax.
