Since Sphere offers so much control in post production does it matter how I position the mic?

Yes, just like any mic, position matters a lot. Nonetheless, the added flexibility can be helpful in many cases. For example, with Sphere technology you can directly adjust the amount of proximity effect of the mic, so you’ll never need to pull the mic back simply because there’s too much boominess from the mic. On the other hand, if there is too much boominess due to where the mic is positioned on the instrument then repositioning the mic might be the only solution.