Real SlowFeeding makes the horse feel better and makes the hay last for longer.
RB Std Low C
RB Std Low C has a mesh size of 4 cm 1 3/4" that is the largest mesh size with any kind of slow feeding characteristics. It is designed to cover a standard round bale from the top down. It fits tight on a 120 cm = 4' round bale. This solution is only recommended when used together with plastic feed rings because if not there is a well-known issue with horses spending all their free time trying to get their heads in under the net.
The actual height of this net is 145 cm = 57" and the diameter is 170 cm = 67" just to make it easier to dress the bale. I recommend you not to consider this net for a bale larger than standard.