= Solution
Retaining the integrated <energy flux> from part (i), slow changes of depth and latitude obey
$$
\boxed{\frac{H A_0^2}{|f|}=\text{constant},\qquad
\frac{A_{0,2}}{A_{0,1}}=\sqrt{\frac{|f_2|H_1}{|f_1|H_2}}.}
$$
At fixed depth and higher absolute latitude in the same hemisphere, $|f|=2\Omega|\sin\varphi|$ increases, so $A_0\propto\sqrt{|f|}$ increases. The offshore trapping width $L_R=c/|f|$ narrows, concentrating the same transported <energy> closer to the coast.
This uses a local Kelvin-mode approximation on a slowly varying background, despite the original constant-$f$ derivation. The scale of variation must be long enough for the wave to adjust without substantial reflection, scattering or dissipation. It is not a rule to extrapolate through the equator, where the coastal trapping scale and hemisphere-dependent propagation rule change.
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