About the tps explanation of pgbench, please help

I am working on a evaluation to put db client outside the datacenter and to
know how the network impact on the business.
After several round of testing, I have a question regarding to the two tps
result in stress output.

Test A:
Client and DB server exist in same AWS datacenter.
transaction type: Custom query
scaling factor: 500
query mode: simple
number of clients: 25
number of threads: 25
duration: 600 s
number of transactions actually processed: 54502
tps = 90.814930 (including connections establishing)
tps = 204.574432 (excluding connections establishing)

Test B:
Client and DB server exist in different AWS datacenter (west and east).
transaction type: Custom query
scaling factor: 500
query mode: simple
number of clients: 25
number of threads: 25
duration: 600 s
number of transactions actually processed: 13966
tps = 23.235705 (including connections establishing)
tps = 42.915990 (excluding connections establishing)

Its obviously that both tps become lower if client and server do not exist
in same datacetner since the network connection have more latency.
But I can not explain why the tps that excluding connections establishing
is changed so much.
For my understanding, tps excluding connections establishing get rid of the
time that create socket cost. That means in above two test cases(only
network different), the tps excluding connections establishing should be
very close, right? Because the database is same and capability is same only
network latency is different.

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Best Regards,

Yanrui Hu (Ray)