Hi Gina,
You would want to move the wheels forward. Moving the wheels forward will improve shoulder biomechanics but also make the wheelchair less stable. This article discusses several aspects of wheelchair configuration, including anterior-posterior axis position of rear wheels: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944313/
Here is an excerpt from the article:
“The anterior–posterior position of the rear wheels influences two important aspects of wheelchair mobility: stability and manual propulsion. While positioning the wheels rearward improves stability, it limits the user’s ability to reach the handrims in this rearward position, thus reducing the push angle. Alternatively, moving the wheels forward improves propulsion biomechanics but reduces stability. The optimal position of the rear wheels is a client-dependent decision, based on the user’s perception of stability and ease of chair propulsion. However, there are some objective guidelines to support this decision. The rear wheels should be positioned in the most forward position that does not compromise system stability23). Gorce and Louis16) showed that, when moving the rear wheels forward, push angle and shoulder ROM are increased, thus reducing both push frequency and handrim forces, minimizing the risk of upper limb injuries32). In addition to the biomechanical benefits, moving the rear wheels forward diminishes the wheelchair length and, as a result, facilitates turning maneuvers by reducing the rotational inertia of the system24).”
Hope this helps!
Chrissy