If you have longer arms, its highly likely the brunt of your work is being done by your shoulders and triceps in pressing. Many folks have also stated, presses are largely a shoulder and tricep exercise. If you want to stick with pressing solely, try pulling your shoulders down and back, more of a powerlifting bench, and that will help to hit the chest more.
Also, don't do any locking out on your benching. Stay in constant tension. Your weight will go down, but you're trying to build muscle, not strength.
Start your chest workout with Hex Presses. This is as simple as taking two dumbells, placing them against each other as you hold them, and pressing them on a flat bench. It will help to fire your chest for later.
If you are willing to do other exercises, flyes are better for long armed guys for focusing on the chest. I also very much like dips personally, but you need to thoroughly warm up your shoulders first. I usually do them after decline bench.
Push-ups never hurt either. Go for volume on these if you decide to do them.
Last, if you increase poundages that's the surest way to add mass to anything. So even if your bench hits your shoulders and triceps a lot, your chest still gets work.