A low position being 'poor-fitting' or uncomfortable is a myth.
Negative side effects of a too upright position quoted from http://www.bikepro.com.au/bike-fit-myth-debunking
Really, If you have some spare time read this article. It's a very refreshing take on bike fitting and has helped me a lot with fitting clients.
1. It transfers most of your upper body weight from your load bearing arms, to your pelvis-spine complex, which induces lumber spine injuries and saddle soreness.
2. Some weight shifts to your feet, as your pelvis-spine complex seeks extra support. Your feet then applies downforce onto the pedals during the upstroke, an undesirable after effect.
3. Your upper body and arms need to work much harder to counter the extra pedaling up thrust when in high loads.
4. With spinal flexion, the geometry of the psoas causes the front rib cage to compress, as there are vital internal organs, the restriction of the abdomen against the thighs limits the movement of the diaphragm, leaving the persons breathing restricted.
5. The lower back extensor muscles (psoas antogonist) strains to counter the spinal flexion, which eventually induces back pain and injuries.
6. This causes your body to be supported by 1 static point (saddle) and 2 dynamic points (feet) instead of 3 static points. (saddle and two hands). As the points are not static, this causes the upper body to need to make constant adjustments to keep balanced, wasting energy.
7. Without both hands to support the upper body, the spine deals with bending moment, shear stress and torsional stress simultaneously
8. The position which allows your body to remove weight from the handlebars, is the setback position, this creates another 20 unintentional consequences.