You're tall and you probably have long fore-arms which means that when you press you naturally form that 90 degree angle between upper & lower arm before the bar touches the chest...but you probably continue down to your chest anyway. This is counter productive.
The awesome trainer Charles Glass said it best in response to someone in a similar position:
"As for what you consider "half reps" on the pressing movements for the chest, I am convinced that doing the top two-thirds of the range of motion is actually much more productive than touching the chest as you've been doing. The reason lies in muscle tension. When you lower the bar or dumbbells all the way down as far as you are able to, you inevitably relax the pecs. You can't help it, this is just how the human anatomy is designed. Relaxing any muscle while you're training it is never a good thing. For one thing, you will fail to deliver the maximum intensity to the muscle; for another thing, you'll expose yourself to a greater risk of injury by forcing the connective tissues to assume the full burden of the weight as you reverse the motion at the bottom of each rep.
That's why a majority of pec tears have happened when guys were bouncing the bar off their chest with a heavy weight. The muscle was totally relaxed at that split second and the tendons had to deal with all that weight and force. Instead, if you keep your chest tight and maintain that good tension on it by avoiding the bottom one-third of the rep, you will be amazed at how much more you feel your pecs working and how much better results you get. I am willing to bet that if you switch to doing your presses my way, you should be seeing some new growth in your chest in under a month. I'm sure it's been a lot longer than that since you saw any improvement there, right? This technique is also very useful for overhead shoulder presses. Give it a try. You have nothing to lose and everything to gain."