Theory: tweeters, narrowest wavelengths, to the insides.
However, in my office, horizontal seated ear height, they surprised me by sounding better on the outside. Probably because it moved the 10" woofer inside away from the left side wall
you simply listen, and take the time to reverse them to decide.
btw, real in/on a shelf bookcase speakers should not have rear ports
This pair was for nostalgia (my first 'real' speakers when in college 1966-70), to be in my garage/shop system. After updating the crossover and two level controls, they sounded soooo good I moved them to my office. Next I bought another pair, updated them, now sounding great in my Garage/Shop system. I highly recommend them to people capable of the easy and inexpensive refurb.
they have separate level controls for the tweeter and mid (output relative to each other and the woofer). easy to get them 'best' in various locations.