WinSAT WorkingBufferSize

Hi,
I've been trying WinSAT on many different systems here and I found something
interesting: if I do not specify the working buffer size (with the
-buffersize command line parameter), it is calculated from some values I do
not know. The documentation here at technet says that
Code Snippet
-buffersize <n>Define the buffer size for the assessment. The minimum is 4K.
The maximum is 2MB. The default is 16KB.

However, the maximum in my WinSAT version seems to be 4KB, and the maximum
32MB. The default value varies from system to system.
I had a workingbuffersize of approximately 8M on an XP sp2 machine, approx
11MB on a Vista32 machine and 12MB on a VIsta64 machine. Why does the
program allocates a different buffer size on different machines ? Wouldn't
it be more logical to always allocate the same buffer size in order to
compare machines ?