This is an JVC autocal thread ... where one is suppose to ask questions about JVC autocal.
That being said ... do you have a calibration disk? Contrast (CR) ctrl sets the brightest white (level 235) without clipping any of the 3 RGB channels. Brightness (BR) control sets the darkest black (16) without prematurely clipping any of the near black levels. Gamma works between the brightest white and the darkest black, but does not influence CR or BR. Gamma will increase or decrease the brightness of "typical objects" in a movie. The lower the gamma, the brighter the objects will be. The higher the gamma, the darker the objects will be. Gamma does not (or should not) affect setting CR or BR. For more details: https://www.avsforum.com/forum/24-dig...l#post46550833
Nat/Std/6500K/2.4 is close to THX only in terms of setting white/blk point and somewhat color temperature (6500K) accuracy. THX goes beyond this and sets color temperature and RGB primaries more accurately. THX will be slightly dimmer picture than Nat/Std/6500K/G2.4 due to the additional calibration performed in THX and that THX uses a filter lens ... the filter lens snaps into place when THX is selected to provide more saturated primaries ... but the lens is darker which darkens the picture a little. You should be able to use either THX or Nat/Std/6500K/G2.2. I would use G2.2 rather than G2.4 if the picture looks too dark in G2.4.
Your HT has bright light reflective surfaces, so use the brightest settings as a default (Nat/Std/6500K/G2.2). Don't be scared to try other settings ... and see what you like better. It's all a matter of personal preferences. You are better off with a slightly brighter setting due to the white ceiling ... but don't make it too bright or you may get eye fatigue and/or you may see some discoloration. There are several ways to brighten the picture: https://www.avsforum.com/forum/24-dig...l#post48241753
The brightest calibrated setting for Nat/Std/6500K/G2.2 is at its default settings (CR/BR=0). This is a very bright setting and many reduce the brightness by reducing the Lens Aperture. If the projector is too bright, one can reduce the LA anywhere from 0 to -15. Your choice.
When people say a light controlled room (a dark room), they are referring to no ambient light shining on the projector screen (from outside sun or a lamp) ... and ... all light reflective surfaces (walls, ceiling, floor) are really dark or black ... like black velvet black ... so no light from the projector bulb is reflected off the ceiling, walls or floor back into the screen. In your case with White ceiling, your better off with a slightly brighter picture because the brighter light will constrict the eye's pupil and will make the brain think it is seeing darker blacks. The light reflection off of your white ceiling is elevating the lowest black level on your screen ... so a brighter screen will help.
As far as Nat/Std/6500k/G2.4 vs Cin/Cin1/xenon/GammaA. Find an outdoor scene with Reference quality 4K/2K blu ray with costumes with highly saturated colors (Gods of Egypt opening celebration scene, Star Trek Into Darkness opening scene (great reds and whites), Kingsman) and pause it. View it under Nat/Std, then Cin/Cin1 ... go back and forth ... see what you like better. Some people like a more natural scene (no edge enhancements nor use of a wider color space other than what the blu ray was mastered in) with a highly calibrated projector (rec709 only). Some like the more saturated colors in Cin/Cin1 because it make the colorful costumes pop more and these colors are closer to what one sees in a commercial movie theater. You need to decide what your preference is. There is no wrong or right answer. Remember, JVC gives you many options to chose from, wider (cin1) and smaller (Std) color spaces via the many color profile to choose from, skin tones and memory colors which look good no matter what color profile you are using, tools to make the picture clearer and sharper, different brightness levels (Lamp Low High), different gamma levels to correct for under or over exposed dvds and blu rays or to correct for bright or light controlled ambient conditions. Can't do any better than JVC.