This is odd on the face of it. The term "ratio" when used in
reference to flash typically refers to the relative intensity of
flashes in a given setup. So, for example, a 2:1 ratio involves
two lights one at (say) f/8 and the other at f/5.6. Bear with me
if you are unfamiliar with using f-stop settings to refer to
light intensity. The point is, one light emits twice as much
light as the other. In a typical portrait situation, a main
light, positioned at 45 degrees to the right of the subject and
a fill at 45 degrees and to the left might be set in a 2:1 ratio
where the main light illuminates and gives definition, while the
fill light softens the image by adding light in the harsh
shadows. Your example is about mixing a controlled light source
(the flash) with an uncontrolled one (ambient). Clearly, the
more flash there is relative to the strength of the ambient, the
less the ambient matters. Expressing this as a ratio, however,
is unusual. But, the "more flash" part can be achieved by using
flash exposure com