When using the shaded circles to plot a sum of net value by territory,
how does mappoint determine where to actually place the circles on the map?
Is it placed in the largest grouping of number of accounts,where the
largest dollar account is located, or is it strategically placed in the
middle of the accounts? I hope this makes sense.

The shaded circles, sized circles, bar and pie charts are all placed on the "centroid" (middle) of the geographic unit (zip code area, county) you are mapping to.