Yes, absolutely! Given a specific fusor, there will be numerous specific limitations based solely on construction issues that will forever limit its capability due to the physics built into the system.
Your insulator will limit your voltage and this will limit its ultimate capability.
Your power supply will, likewise, limit its capability.
Cleanliness of the running system as well as small fit and finish items will limit capability as well.
Opearator issues are always a big limiting factor.
The longer one spends with a demo fusor in study and reading, the better his first pass at fusion will be. Star mode in a demo device usually signifies good assembly and vacuum system skills. This usually signals that one is skilled at some minimal level of operating in fusion mode.
Once fusion is achieved, continual operator familiarity with the system, any system, will pay off in increased capability of that system up to it "glass ceiling". This is the point where the operator is so familiar and skilled with his system that no more artifice in opertional practice will move the system higher. At this point the failure to improve falls back on the design and power supply which are, now, doing all they can do.
From this point very minor physical upgrades will most certainly improve the systems capability. One of the most significant boosts would be to get a new supply and HV input insulator to allow for increased operational performance. Usually, a bit more learning at the controls will be needed to get used to the bringing up the fusion level in the new environment.
The upshot is to plan ahead so that the glass ceiling is about where you wish it to be in the construction phase and pray you can master the system, operationally, with practice to reach that glass ceiling provided by a properly designed system.
Good luck to all.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.