It could be cooling related, it's a straighter path for air piped to caliper if it were at the back, than if the piping has to curl to the bottom.
What's more if this cooling was not being distributed evenly on the caliper then there might be uneven expansion of the caliper aftecting the performance and reliability.
It seems the air can be more evenyl distributed if the caliper was simply downstream instead of around a bend. Other than that it could do with the electronics positioning as well.