Hi in new to forums
I have been playing Kerbal for some time just noticed that all rockets have Specific Impulse (Isp) always lower for Above Sea Level (ASL) than (Vac.).
From what I know rockets are quite efficient and the only difference is mostly in the nozzle design.
https://en.wikipedia.org/wiki/Rocket_engine_nozzle
See ideal expansion. Hence it must be possible to have rockets that are designed to be more efficient in atmosphere.
Seems like this has not been implemented.
It would be nice to see some lower stage rockets/engines.