JVC RS-46 :: Smaller throw distance results in darker picture ? (1 Viewer)

Hi guys. I'm facing this 'issue' of sort which I wanted to discuss. I'm trying to decide where to place my JVC RS-46 in my HT room, and have to pick from one of two potential locations. I placed the projector in both locations yesterday (using cardboard boxes to hoist the projector up) to see how to picture looks. It seems that pictures generated from the FURTHER of the two locations is brighter in majority of the cases, whereas it should have been the other way around ..


Here's how I did the test:

>> Using a DSLR, I took pictures of the exact same video frame from both locations
>> I used a tripod to ensure DSLR doesn't move
>> DSLR's autofocus was disabled
>> Saved pictures in NEF format to get RAW untouched pictures for making comparisons in Photoshop
>> 14 scenes were captured from both locations
>> The first of the 14 uses 'Natural' setting defined in RS-46 (PS3 XMB Screen), while the remaining 13 (Avengers 3D Blu-ray) used the default '3D' setting
>> Screen used is a 119" 16:9 Da-Lite HD Progressive 1.3 Gain screen
>> Tripod was about 6 ~ 7 away from the screen, in the center of the room

Everything shown in both drawings below is to scale.

Position A (Throw distance: 15.5 feet):



Position B (Throw distance: 12.5 feet):



Open Spoiler to see comparison GIFs:


Results:

>> In 9 pictures, I found Position A pictures to be brighter (to varying extents)
>> In 4 pictures, Position B's pictures were brighter (to varying extents)
>> In 1 picture, both were equally bright
>> In some pictures, Position A's result also looked better, e.g. more accurate skin tones, color, etc.

Questions:

>> Can someone explain this anomaly to me ?
>> Maybe there's some variable I may have overlooked possibly ?
>> Or should I trust these results and put the projector at the further of the two distances ?

Position A is straighter. Resulting in more light bounce. (Just look at the greater angle of the bottom of the light beam in B. I bet A results in a clearer image)

It is common knowledge that using lens shift results in slightly less brightness. And your distance difference, in reality, isn't much(with that projector).