i don't think so...
let me explain how raw data is stored in memory for resolution 1600 x 1200
for 1 bitplane, each 1 pixel is represented by 1 bit...
so in one scanline there are x/8 bytes means 1600/8=200 bytes
for 1200 scanlines there are y*scanline bytes of data for each bitplane 1200*200=240000 bytes
since the resolution is 24 bit for [R8,G8,B8], all bitplanes cost 240000*24=5760000 bytes (5.49 MB)
The above calculation is for raw 24 bit image data.
MXI is not a 24 bit image data.
It's a more precise spectral data and not stored as bitplanes.
MXI is derived to bitmap for viewer.
The constant you found (112) should be giving you a hint about it's precision about each pixel 
..and 215 MB is 215*1024*1024=225443840 bytes.
therefore your constant must be 117 something 
