No Worries Spennie!
On my high racer 26/26 the seat is at 20* and there is just enough clearance between the wheel and seat for the bag.
with the mudguard on and bag full, it rests on the mudguard, but not a problem.
if you only have a couple of inches to spare, then the radical solo racer bags may be ideal as they hang either side of the wheel, I have these on my lowracer as there is no room between seat and wheel.
Take care,
Barry ;-)