Kohler Transfer Valve

I am in the process of remodeling my bathroom. I am installing a Kohler 3 way transfer valve after the shower valve body to feed an wall mounted slide bar handheld shower head(along with a regular wall shower head). The installation instructions tell you that the supply to the 3 way valve needs to be 3/4". I am not sure which is the correct way to plumb the shower valve body to the 3 way transfer valve. Do I install a 1/2" to 3/4" adapter at the shower valve body(positoin b on the drawing) and run 3/4" pipe to the 3 way valve or do I install a 1/2" to 3/4" reducer at the 3 way transfer valve(positoin A in the drawing) and run 1/2" piping from the shower body to the 3 way valve?

Another question. The installation instructions show a union or a threaded connection at the 3 way transfer valve supply. Does anyone know if this has to be treaded or can I sweat in the pipe/fitting(depending on the answer to question above) like the other outlets from the transfer valve and shower body?

I've attached a picture to help out.

I have a post similar to yours that you posted on. I talked to Kohler again and got a rep that really knows his stuff. He said that the pressure drop will not happen as I was previously told. With regard to your question, he said to use a copper fitting that is 1/2" sweat on one side and 3/4" NPT female thread on the other side which will be threaded to to the diverted valve inlet. Are you planning on using a 304 mixing valve and a 672 transfer valve? That is the configuration that I plan on using.