Mqtt & Sensor example - PSM Mode on nrf9160dk

Good day to all

I am at the final stages of developing a program for collecting sensor information from a UART and publishing it onto a mqtt server.  Currently the device is running at 22mA before it enters PSM mode and  at 660 uA when in power saving mode.  Ive also experimented with the standard mqtt_simple sample in PSM mode and it is around 500uA when in power saving mode.  I was hoping for a lot smaller and was wondering if it is possible to go lower.  Is there anything I can change and if so, how can i do it?  Thank you .

Kind regards,