Why block_size_n equals page_block_size

I see in flash_api.cpp, you hard code block_size_n  as PAGE_BLOCK_SIZE. I dont think there is any constraint force those two variable equals. 
    params.block_size_n = Config::PAGE_BLOCK_SIZE;

If you simply write this equation because you only support block_size_n = 64 and page_block_size = 64, I can later push a PR to support more page_block_size (such as 1, 4, 16)