Size of file in file system

Dear all,
After implementing file system on both 1Gb Nand Flash & 4Gb Nand Flash, using LPC1788, i found that the minimum size of any created file was as follows:
1Gb - 8KB
4Gb - 16KB

I want to decrease the file size to 4KB only. If you know any possible way, kindly highlight.
I tried to search for any related document in keil's documentation but could not come across one.
The minimum size of a page in both the Nand Flash is 2KB (incase this data is of any relevance).

Regards,
Dhaval

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