Two rear tubes, each with 20 patches now after today. My current isolation ride, of about 2 hrs uses an old railway line and canal path. Both extensively cut recently, hence all the punctures. No point on putting in a new tube until the route clears a bit. Get between one and four each ride at moment, but not had to patch during the ride - usually find the flats each morning before the next ride.
Only 5 patches on the front, so at a ratio of 1:4, the rear is clearly much more prone. presumably the weight, and it being driven forces the thorns in more efficiently on rear.