Hi Keith,
I don't know who wrote the article you read but there is no 'ideal' or perfect length to width ratio for catamarans. Catamarans of all length to width ratios can be pitchpoled and turned over sideways. The responsibility to avoid these undesireable situations belongs to the sailors on the boat. For turnover the sailors on the boat can see and feel the windward hull lifting out of the water and the boat tilting prior to turnover. They are being given notice. The wider the boat the more slowly this action occurrs and the more time is available to take corrective action and avoid the turnover.
Pitchpole is more subtle but there are signs that the boat is getting close to pitchpole such as the bow being driven lower and lower until it goes under solid water, not foam or spray. At the moment the bow and foredeck go under solid water there is an abrupt increase in hull drag and the boat stops quickly and does a forward cartwheel maneuver. So to avoid pitchpole, watch the bow!
Hull design has much to do with pitchpole. The taller the bows, the more wind it takes to make a boat pitchpole. The more streamlined the foredeck is, high arch side to side, the smaller the increase in hull drag when the foredeck is pushed underwater. Hulls designed with a flat foredecks pitchpole with a snap roll, very quickly. Hulls designed with a foredeck that is shaped with a high peak in the center will pitchpole much more slowly, sort of a mushey pitchpole. Sometimes this hull shape will recover from a near pitchpole situation even when the transoms are 4 or 5ft up in the air if the sailors can hold their positions on the boat and not fall forward.
Bill
PS. I put a SC20 together once that was 20ft wide and it sailed fine. To windward it was a rocket. Reaching don't trapeze. Downwind same as a normal SC20, watch the bows.