It seems absolutely reasonable to me that two stations in the same system would interact. I'm really struggling to see how that could be unreasonable to anyone.
Although if you went down the realism nerd rabbithole further, one could point out that trading between Foo's Folly in System Alpha, 127ls out, and Baz's Bastion in System Omega, 96ls out, is actually way more efficient than Foo's Folly trading with Wotsit Vision out around System Alpha's B star, 435,275 ls away, if Systems Alpha and Omega are one short high-wake apart.