Shared Pool on statspack report not what is set in shared_pool_size

Oracle Database 19C (19.13) on Linux

I'm trying to understand what I should be tuning to affect my shared pool size.

Here are some of the parameters that are currently set:

memory_max_target		0
memory_target 			0

lock_sga			FALSE
pre_page_sga			TRUE
sga_max_size			34359738368	(32G)
sga_min_size			0
sga_target			30064771072	(28G)
unified_audit_sga_queue_size 	1048576 

shared_pool_size		4294967296	(4G)
shared_pool_reserved_size	429496728

When I run my statspack report I see:

...
Cache Sizes      Begin    End
~~~~~~~~~~~    ---------- ----------
  Buffer Cache:   6,080M       Std Block Size:     8K
   Shared Pool:  16,256M         Log Buffer:   4,096K	
...

I have a few questions:

• How is the actual shared pool size of 16G getting calculated?