The Su-27 stabilisers pivot about an axis that is approx half-chord.
The actuator is in the fairing at the base of the fin - the triangular section of which is attached to the stailiser and slides in and out of the fairing at the base of the fin.
At rest, most Su-27's have the fin leading edge raised - with a corresponding amount of the triangular fairing exposed.
The Hasegawa (and Revell re-box) have the stab mounted horizontal - to be correct you need to remove the locating tab from the stabiliser, and add a pivot from rod - with a corresponding hole in the side below the fin.
Then mount the stabiliser at an upward angle. You then need to remove the triangular fairing from the base of the fin - and attach it to the stabiliser.
You may need to add a triangular wedge from plastic card to fill the gap between the fairing and the fin.
There are some photos of Flanker fins on my website at :-
which should explain the arrangement better than I have...
There are also some of my articles on making Flankers at :-
I hope this helps......
Flanker Freak & Russian Aviati> I'm building hasegawa's Su 27.