  The phase difference $\phi$, between the superconducting terminals in
superconductor-normal metal-superconductor tunnel junctions (SINIS),
incorporates the phase differences $\chi_{1,2}$ across thin interfaces of
constituent $SIN$ junctions and the phase incursion $\varphi$ between the side
faces of the central electrode of length $L$. It is demonstrated here that
$\chi_{1,2}$ pass through over their proximity-reduced domain twice, there and
back, while $\phi$ changes over the single period. Two corresponding solutions,
that describe the double-valued order-parameter dependence on $\chi_{1,2}$,
jointly form the single-valued dependence on $\phi$, operating in two adjoining
regions of $\phi$. The phase incursion $\varphi$ plays a crucial role in
creating such a behavior. The current-phase relation $j(\phi,L)$ is composed of
the two solutions and, at a fixed small $L$, is characterized by the
phase-dependent effective transmission coefficient.
