Please note that the captrim is available only for the ECO i.e to set the frequency. So it cannot be used to tune the Antenna/RF path to recover the lost range.
You can use external power amplifier/ modify the mechanical structure of our design to improve the range.
Can you please attach some images of your board? We would like to see if we can provide some guidelines. Please refer our appnote on Antenna design guidelines from the link below: