Why does my Epson HX-20 apparently have much less RAM than expected?

When I enter:

STAT ALL

On my Epson HX-20, I get the following output:

P1: 419 BytesP2: 86 BytesP3: 0 BytesP4: 0 BytesP5: 0 BytesRAM FILE 256 BytesMEMSET 2624    105 Bytes Free

As I understand it, even a standard HX-20 should have 16k of RAM, so the Bytes Free should be much more. I also remember writing much longer programs in the past than I am able to now before getting the OM (Out of Memory) error.

I have looked up the MEMSET - the above is the factory default and should give maximum space to BASIC programmes as I understand it.

Can anyone suggest why I might be having this situation, and what steps I can take to rectify it?