I'm not! Your coil size was better suited to this particular target than the larger coil.
The 6.6KHz frequency was closer to optimum and only had to analyze this one freq.
The coil on the White's was optimised for 6.6KHz - when the SMFs use one coil for all frequencies,
they are less sensitive away from the optimum frequency of the coil, which I doubt in
this case was 6.6KHz or below.

There's a lesson to be learned here. SMFs are not ALWAYS "king".
There is an optimum frequency for each coil, and using that frequency,
the detector has its best sensitivity. i.e. X-terra. Not to say that
X-terras are the most sensitive detector there is, just that given a coil
that is optimised for the frequency in use gives it an advantage.

I don't know anything about the X-terra "pro", but if it uses one coil
for all usable frequencies, i'd be a little wary of it. It *appears* to
be a stripped down Equinox.