It is to the south, because the galactic north-south axis is perpendicular to the plane of the page. I guess you mean more to rimward and spinward. But that wouldn't work because it would put the Expanse too close to Ceti Alpha. And the Expanse was said to be 2000 ly across, not 10,000. Although "The Xindi" complicates things by having a member of the Council say Earth is only 50 ly away, which is inconsistent with the lengthy travel time specified in the previous episode. I think we have to discount that reference (maybe a Xindi year was much longer than an Earth year). True, fitting a 2000-ly-wide region into a galactic disk only c. 1000 ly thick is tricky, but maybe it's a relatively flat region, hugging the southern face of the disk. (There was no indication that the Expanse extended into the relatively starless region beyond, and then there's the Barrier to consider.) Although then it would have to be far wider than shown in the new map, pretty much extending "beneath" the whole depicted territory. Still, other than that, the position selected is very logical and seems like the best fit to the canon evidence.