What User Mode are you in? I would suggest Cinema or User 3.
Plus, try taking readings with Iris OFF instead of Manual @ 100. I found out the hard way that they can have different white balance presets in the Service Menu.
I would be surprized if the room effected your readings THAT much, but if they are white and glossy it may be. How far away from the screen is your meter when taking measurements? Sounds like you might be in a very small, square room. If so, You could try a LOW lamp setting so you aren't creating as bright secondary reflections.
You could get a handle on what is potentially happening by taking a look in the Service menu under W/B for each of the color temp settings (HIGH, MIDDLE, LOW, CUSTOM1. CUSTOM2 & CUSTOM3) just make sure you note which Iris mode you are in since those values can/will change depending on whether you are in OFF, MANUAL or Auto.
JVC X750R, 133" DaLite HP (2.8 gain), OPPO UDP 203
Denon X4300H, DIYSoundGroup Fusion 15 L/C/R, Mirage FS V2 Surround, Mirage Omnisat V1 Surround/Atmos