A little bit surprised at this statement as because the reversers operate in the vertical plane its going to be stirring up a lot of FOD that is likely to end up in the engine intake.
They use a chalk test to determine relative reverse thrust levels vs aircraft speed to visualize the reverser efflux flow and potential for ingestion.
These visuals show that the small pieces of chalk are blown forward off the tarmac too far to be ingested especially when the aircraft is backing up.
At high landing forward speeds they are overrun before they bounce off the runway unless of course you eject too much efflux at lower speeds. If this is the case then you definitely want to be over a runway blown clean by other aircraft operations