  Every now and then one can hear in the molecular electronics community that
asymmetric couplings ($\Gamma_{s} \neq \Gamma_{t}$) of the dominant level
(molecular orbital) to electrodes ($s$ and $t$) which typically have shapes
different of each other may be responsible for current rectification observed
in experiments. Using a general single level model going beyond the Lorentzian
transmission limit, in this work we present a rigorous demonstration that this
is not the case. In particular, we deduce an analytical for the bias ($V$)
driven shift of the level energy $\delta \varepsilon_{0}(V)$ showing that
$\delta \varepsilon_{0}(V)/V$ scales as $\Gamma_t/W_t - \Gamma_s/W_s$, which is
merely a tiny quantity because the electrode bandwidths $W_{s,t}$ are much
larger than $\Gamma_{s,t}$. This result invalidates a previous, never-deduced
formula in use in some previous publications that neither could be justified
theoretically nor is supported by experiment. To the latter aim, we present new
experimental evidence adding to that already inferred in earlier analysis.
