Hi Mark, it is always recommended that you use the same diameter hose/piping as the suction and discharge ports on the pump. While it is sometimes necessary to reduce that diameter, it is strongly advised that you do not reduce the hose size by more than half an inch.
While you may see an increased pressure due to the slightly smaller piping, this will also see an increased backpressure on the pump. The more you reduce the hose/piping diameter, the more you increase this backpressure and likely cause the pump to fail and that would not be covered under warranty.
Cheers, Steve