considering just this line:

define('BX_DATA_INT', 3); ///< integer date type

the weight of your comment is nearly equal to that of your required source?
source = 25 characters
comment = 24 characters

so with this concept you are increasing the file size on all declared variables and constants by nearly 100%

so lets look at even the use of the BX_ could you not write a constant that would prepend the BX_ and take out those three characters being declared each time?
or substitue see more the entire BX_DATA declaration
this eliminates 7 characters if you can manage that one. i know it seems trivial, but increasing a file size just for specified comments doesnt seem like its driving in the direction of decreasing the footprint and/or optimization performance?