I hit water more frequently then I hit max brake power. So I'll stick with keeping the tread in the direction it was designed for optimal traction rather then trade it off for a slightly possible scenario of lamination separation.
Here's the thing, if you compare a rear tire tread to a front tire tread you can see that the siping is exactly opposite.
As a double-darkside novice (about 70,000 miles ago, on two bikes), I compared the rear tire's tread (in this case a Pilot Activ) with a front E3 tire.
Since I ride in a LOT of rain, I wanted the siping to channel water just like the engineers envisioned. In the photograph, I
matched the siping direction which means the rear Activ got
mounted reversed from the arrow.
I care not a whit about belt plies, tread splice, braking force, etc. I
would like to see the BT45 pictured just like below for siping comparison. For what it's worth, my 93 GL1500 delivered 36,000 miles on its first darkside front tire. It would have passed state inspection tread-wise, but I replaced it as a maintenance convenience rather than take it off the road for maintenance again later on.
Disclaimer: I don't own an ST (yet) but I have lots of miles darkside and double darkside on my Valkyrie IS and
all double darkside on the 93 GW, currently >49,000 miles on that bike alone. I never did ride the 93 on standard MC tires, other than a quick neighborhood test ride when I bought it.
My only hydroplaning incident was on the 93 when its first rear Austone Taxi tire was just getting close to the wear bars in the middle tread. The front held steady as a rock, but I could feel the rear wandering off track at right about 50 mph in a gully-washer downpour. The water was pretty deep on the interstate when that happened, twice on the same stretch of road. Twice because I just HAD to recreate it after the first incident- which got my attention, big eyes - with an immediate steady throttle roll off as I covered the rear brake pedal, but never pushed it.