Heap size of G726 Encoder and Decoder

Hi all,

I downloaded from the page of the TI G726 Encoder and Decoder c55xx, but there are questions.

http://software-dl.ti.com/dsps/dsps_public_sw/codecs/C55X_Speech/index_FDS.html
 G726 Encoder and Decoder, Version 2.00.00.012

For G726 Encoder and Decoder is set to 0x800 the size of the area of HEAP linker,
operation was unstable, and when increased to 0x1000, behavior is stable.
I want to know the recommended value of heap size.

Regards.