Yes Mr H, you are quite correct and I have swapped only the fronts contrary to Audi's advice. Audi's advice is not always perfect. I work on the basis that 2 winter tyres are better than none and of course I know that 4 is better than 2. I can recall a few winters ago, 2012, when we had a shed full of snow (I mean lots of standing snow). I put snow tyres on my Ford Galaxy (front only) and the transformation was amazing. I could go virtually anywhere and drove faster than most 4wd vehicles. In snowy conditions, its traction to get going, steering to give you control and braking to stop you that is required. On front wheel drive cars, the snow tyres get you moving and if you want to stop the front wheels do 80% of the braking, so its fine. I also had fun going around roundabouts and if I went faster than normal I could feel the back end slipping sideways, so knew the limitations.
Now for 4wd, its a bit different, because the rear wheels do half of the pushing and in snowy conditions, there is a chance that while accelerating, the back end could spin you round, but then that would also be the same if you had 4 summer tyres. So until it snows, I am fine with 2 winter fronts tyres. It gives me improved traction and improved steering in slippery conditions which to be honest, I have not yet experienced in cold wet conditions. As soon as the snow arrives, I have 2 more snow wheels and tyres in my garage and I will put these on the rears to be totally safe. Unfortunately, I bought the car and spare set of wheels and tyres in 2014 and sod's law means that it has not snowed in Hampshire since then, so my rear tyre calculations on wear are correct .
MOT is coming up soon and Audi will no doubt tell me the same story. No doubt others will have a view on my wisdom or lack of it.