Think Starbucks Venti (20 oz) cup here. The holder is larger than the diameter of the cup and since the cup is tall it tends to tip over easily. The cup is 62mm (bottom diameter) / 88mm (top diameter) / 152mm (height).
http://www.completemerchandise.co.uk...per-cup-sizes/
A 16 oz plastic solo cup is 63.5mm bottom diameter, 92.25mm top diameter, and 120.65mm high. These widen out enough they don't really move much in the holder and the largest Starbuck solo cold cup locks in pretty tight.
My prior car, a MKV gti had a cupholder that was 77.35mm diameter at the top and 59mm deep. It tapered slightly toward the bottom but I can't say how much. This cupholder was nearly ideal for paper coffee cups of all sizes.
I don't have my calipers to measure the BRZ cupholder but it's bigger in a non-helpful way.
This is suddenly getting kindof involved but in a good way.