I have mine (Sirius Sat) right next to my rear-view mirror. No interference with the rain-sensing wipers. Longo Lexus of Los Angeles installs Sirius in all of their cars for free, so they have tons of experience enabling Sirius on Lexuses. The RX400h next-to-rear-view-mirror install looks pretty good (out of way), and reception is great.
Where is the radio itself situated? On the dashboard? If so, how do you avoid having a hanging cable from the rear view mirror to the dashboard? I have kept everything on the dashboard to avoid that kind of problem. Also, the suction cup never worked. The radio kept falling down. I finally mounted the radio on the dashboard with sticky Velcro, hid all the cables (except the absolutely necessary connecting power cable and antenna cable) in a black leather box, and put that on the dashboard as well, Not very elegant, but it works like a charm.... sort of.