Specify what you mean in regards to contact patch increases as you lean over. A lot of available traction, what your calling contact patch, depends on tire profile, tire compound, suspension set up, accelleration inputs, braking, etc. The important thing about the contact patch is how much force it can transmit before losing traction. The more you lean, the more you force your contact patch to transmit. When the bike’s completely upright, you are increasing the bikes stability and available traction because less force is being transmitted through the contact patch. And you carry more corner speed by increasing your bike’s stability… that’s why they tell you to take care of your braking, shifting, etc. before entering the corner.
Hanging off on the street would be a personal choice. In the rain, I definately recommend it. I personally, hang off even when not exceeding the speed limit. You don’t get points on the street for lean angle.