Performance tuning/Response times in Postgres 11.2

Hello Experts,

We are running our application on PostgreSQL version 11.2 on Centos 7 OS.

Have updated below performance related parameters for a 36 vCPU and 72 GB
memory instance and recorded response times.

shared_buffer=14GB

effective_cache_size=50GB

random_page_cost=1.2

work_mem=128MB

maintenance_work_mem=512MB

Now I have upgraded the machine to 72 vCPU and 144 GB memory with below
parameters:

shared_buffer=36GB

effective_cache_size=108GB

random_page_cost=1.2

work_mem=256MB

maintenance_work_mem=1024MB

And performed the same testing and to my surprise the response times are
almost similar and there is no improvement even I am running on the bigger
machine.

I want to understand if I am missing any basic settings that is causing the
slow response times ? Please shed some light here.

Thanks,

Srikar