  Although the enhancements in the alpha-proton ratio in the solar wind
(expressed as $A_{He} = N_a/N_p*100$) in the Interplanetary Coronal Mass
Ejections (ICMEs) have been studied in the past, $A_{He}$ enhancements at the
stream interface region received very little attention so far. In this letter,
by extensively analyzing the stream interaction region (SIR) events observed in
solar cycle 23 and 24, we show that the stream interface of alphas starts
separating out from that of protons from the minimum of solar cycle 23. The
population of alpha particles are enhanced compared to protons at higher angles
between bulk velocity and local magnetic field (henceforth, bulk velocity
angle) in the fast wind region of SIRs if the background solar wind is taken as
reference. The analysis of differential velocities between alphas and protons
also reveals that the faster alpha particles accumulate near the fast wind side
of the stream interface region leading to enhancement of $A_{He}$. The
investigation brings out, for the first time, the salient changes in $A_{He}$
in SIRs for the two solar cycles and highlight the importances of bulk velocity
angle and differential velocity in the fast wind region for the changes in
$A_{He}$ in SIRs.
