Posture and sunk diaphragm.Sitting low is it good for all?

I really don't know how to start this thread. I have been reading your blog Mr Fraser,and i was very happy to read the thread about breathing and piano. Here is the problem i have.If you remember from a previous thread i had the problem that i could not have the piano bench low enough because my knees would be literally in the air and even higher than my back when i sit down. The solution was to put pieces of plywood and raise the piano so i could sit higher yet my hands to be a little lower without the knees in the air problem. However it is still not possible for me to solve this.I haven't found a way to deal with the pedals,my piano tuner told me that if i raise the piano then the pedals would be way up. So i had to abandon the idea of raising the piano,(by the way i dont have a concert grand only a good yamaha u1 upright). Second problem is with my diaphragm. If i raise the piano bench my arms are very high and in positions i am not used to play like this(but i have seen many great pianists do place the hands so high!).I feel like i am cheating by using less muscular effort to raise arms. In that case my body is so well aligned but my sound is gone!I have "finger" speed,but dynamic control is gone.Those flat finger style passages with a heavy fortisimo ala Horowitz can't be easily done if one is high in the air. If i sit normal i feel that my diaphragm is hard pressed down,and inhibits my normal breathing.I feel like my inner self (literally my organs,my diaphragm) is pressed down hard and i am cut in 2 halves.I try not to slouch not to tense.But i can't breath normaly!.I try to breath normal but there is tension in several areas of my body that is probably related with the bench height and i can't do much,unless i raise the bench! Temporary solution for me was to raise the bench about 7-8 centimeters.That helped but i still feel the problem of a tense collapsed diaphragm So i assume that sitting low is not beneficial for all of us?Could there be an exception? Every day i feel like i am literally fighting with the keyboard,i am using my consious efforts to reduce muscular activity and let the skeleton play more.But it seems to me that all i do is that i slowly practice and torture myself into a position that is not beneficial for me.I feel my breathing has problems. When i am upright walking and doing all sort of stuff like all human beings do i have no problem with breathing,when i sit down i feel like my diaphragm is collapsed tense,and then everything tends to seize up. I am trying to perfect my playing and remove all these problems,by curing the internal tension that causes bad performances in my piano playing. Low sitting versus high sitting?Could you post a blog entry regarding this? Shouldn't piano manufacturer's help pianists by making a mechanism that would lower or raise the keyboard ? Thank you for your wonderful forum mr Fraser.