I think Larry's advice is well given.
As Mark pointed out we will certainly pay attention to having the appropriate guards in place to do this safely but somebody else reading this thread might have less experience than us and might not include the extra safety. (If I think to my early years it's amazing I still have all of my fingers.)
We've been doing this operation successfully for quite a while with the cove cutting from the bottom of the piece. We have finger boards in place and this has been a hand feed operation. For some reason, however, on the most recent job the MDF tenons were a little tight.
The only thing I can surmise is that we either got an oddball piece of MDF in the building or else maybe all the rain of late has caused it to swell just slightly. Another possible culprit might be degradation on the carbide router bit. It might be showing some wear which could also account for a change in final thickness.
I have had a power feeder on the radar for this operation for some time now. To use a power feed we would need to have the flat portion against the table so that the power feeder didn't rock the blank as it fed against an already coved side.
I see this spinning into a thread about bucket brigade manufacturing so I should probably stop before I hijack my own post.