My own theory, and I have no way to prove this, is that as long as the backwash flow rate is higher than the filter flow rate, the filter should backwash just fine. Logically, it just seems like if there is a certain force the embeds dirt into the sand, then an equal or greater force should be able to liberate it. And since backwash mode usually has much less head loss than filter mode, backwash mode should always have greater flow rate. But enough of theory.
A few manufactures have recommended a flow rate of 15 GPM/sq-ft but I have also heard that down to 10 GPM/sq-ft is also acceptable. But assuming that the higher number is the target and the filter area is 4.9 sq-ft, then the backwash flow rate would be about 74 GPM. The CMF 1000-H will deliver 74 GPM around 50 feet of head. For backwash mode, this should not be a problem in most setups but it depends a little on the suction side plumbing setup (run lengths and pipe diameter) plus the backwash valve size all which contribute to head loss.
IMHO, I wouldn't worry about it.