Flushometer Rough in height

I work at a facility that recently had a bathroom remodel. There was never an issue with the plumbing backing up. After the remodel the plumbing has already backed up 3 times in a month. The flow rate of the new toilets and flushometers is the same as the old. The rough ins for the new toilets are only 10 inches above the fixture. The spec sheet for the flushometer says rough in should be at lease 11.5 inches above fixture. The flush seems to have good pressure and flow. Nothing gets stuck in the bowl. It all gets into the sanitary pipe and then backs up. My question is this; could that 1.5 inches lower on the rough in be responsible for reduced flow or pressure. Enough to cause the new backups?