The oral bioavailability of Clonazepam (Klonopin; Rivotril) is approximately 90%. Finding clear information regarding the rectal bioavailability of Clonazepam is pretty difficult unfortunately. I am taking a completely wild guess in saying that I expect the rectal bioavailability to be pretty close to the oral bioavailability, which itself is actually pretty high. I wouldn't expect a large difference in potency of dose mg for mg, but you'll have to find out for yourself. It could at most be 10% higher than the oral route, so, go by that.
However, the rectal route of administration often brings with it a slightly different feeling than the other routes, but I think all of the different ROA's have their own character. The faster onset and quicker peak of effects could lead you to interpret this as a dose being stronger than it truly is, if that makes sense.