I have a 150 furling genoa on my boat and have found, contrary to what appears to be "common wisdom," that I can roll up this sail to just about any size I want and the boat will still perform well. Long distance cruiser Webb Chiles has written about his experiences with rolling up his headsail to a mere hankerchief when needed. But first things first: the reason you reef is that the wind is up and want to maintain a safe speed and boat control. While my rolled up genoa begins to lose shape at the luff due to the bulk of the sail rolled up on itself, the shape of the sail exposed to the wind is really of little concern to me once my boat is doing hull speed. No matter how I might "improve" the shape of that rolled up sail, my boat is not going to go any faster -- all it can do is go slower. For example, I have sailed my current boat in 30 kts of wind with one reef in the main and the genoa rolled up to about 40 per cent (which approaches the size of a storm sail). Boat was cooking along at over 7 kts. I can't do better than that.
I've also found that my boat will sail farily well, albeit slower, with only one or the other sail up, I've also found that any "slot" is better than no slot.