Please refer to this article to know more about Speaker sensitivity. explained very clearly.
Understanding Speaker Sensitivity - Geoff the Grey Geek
A simple explanation on how to understand and use Speaker Sensitivity specifications. Includes calculators to determine how loud your speakers will be.geoffthegreygeek.com
I use Castle Knight 5 floorstanders having 91db sensitivity and they provide good bass even at low volumes.
This is also very basic along with Sensitivity, impedance curves and Phase curves also make a very bg difference. you can have a 90db speaker but if it drops to 3 ohms at 40 hz, you will hear a lower bass at lower power since most amps dont hold current across curves. A phase swing due to crossovers can also do the same.
Hence lower volume listening has a lot to do with everything. Speaker-Amp Matching, Room setup ,components,vibration control, power and even ambient noise and not something you can fix in a short term unless you are really experienced to know the interplays.
Late night listening usually reduces a lot of these parameters and is a good judge since power improves and ambient noises reduce and you are only left with inherent noise of the components ( which again is higher in most tube equipment )