The move will work the triceps to some extent, because one of the functions of the tricep muscle is bringing a straight arm behnd the back (which, if you translate that into a lying down posture, is akin to the last part of the pullover).
Some ideas:
You may just have weaker triceps proportionate to back, and they need to catch up a bit.
You may be bending and straightening the arm somewhat during the move, which will call on one of the other functions of the triceps (straightening the arm. The third function is turning the arm from supine to prone). Make sure to keep the arms in a locked position.
Put the mind in the muscle (very necessary on this move, IMO, as it can target the back or the chest, and sometimes that focus can help make the difference). As you are bringing the bar from behind the forehead to overhead, push your scapulae into the step to help engage the back muscles more. Try the move with very light weights, or even no weights, to train yourself to engage the right muscles. If you are doing it, you will feel the move even with no weights.
Don't bring the bar any farther 'forward' than over mid chest. Any farther might start engaging the triceps more.
HTH!