Confused about the buffer pool size

In the code (costsize.c), I see that effective_cache_size is set to DEFAULT_EFFECTIVE_CACHE_SIZE.

This is defined as follows in cost.h

But when I say 

show shared_buffers in psql I get,

In postgresql.conf file, the following lines appear

shared_buffers = 28MB                   # min 128kB

           # (change requires restart)

#temp_buffers = 8MB                     # min 800kB

So I am assuming that the buffer pool size is 28MB = 28 * 128 = 3584 8K pages.

So should effective_cache_size be set to 3584 rather than the 16384?

Thanks,

MMK.