I am proposing negative ram. The tailpipe is dramatic, but the gas comes from somewhere, in the case of the over square intake, cool air comprises more mass than the exhaust. If you could paint the exhaust red, and the intake blue, the huge blue cone in front of the engine is lower in pressure than the small red cone in the back. The aircraft is falling forward into its own 'blue hole', and the front of the intake disc is massively more involved in propulsion than the doughnuts on a rope in back.
Pratt/Whitney. J58.