What are the PROGMEM or static memory limits on MKR1000

I am using a Firebase library with my MKR1000 which has a large of amount of data stored as static constants and in PROGMEM

If I add in an image in my program as static const uint8_t or store in PROGMEM my application compiles but fails at runtime once I load the image on a TFT screen. The image size is 4k (64 by 64 bytes).

Now, if I store the image as a global variable uint8_t my application works fine.

So I wondered what is likely to be the problem as was not expecting this runtime behaviour. Is this a static or dynamic memory allocation issue etc.