Vent stack arrangement
I am remodeling my home bathroom. It is 55 years old, raised foundation, single story, California plumbing code, with cast iron waste lines. The cast iron is heavily corroded inside & out so I am replacing it with ABS. (It is easy to work in the crawl space during this remodel because I had to pull up all the floor boards due to water damage. I can easily reach all the cast iron while standing between the open joists!) The bath remodel moves the sink and shower so I can't just copy the original layout of the waste lines. The toilet is back-to-back with another toilet in the adjoining bathroom. The 3" main stack/vent is in the wall between the toilets. The two toilets will dump into the stack with a 3"x3" double sani-T. I also want to drain the sink and shower into the main stack via another double T that has 2" inlets on opposite sides. The sink is re-vented into the main 3" vent at about 40" from the floor. The shower drain will be 3 ft from the main stack so 2" pipe from the shower trap to the main vent should be good without another vent line for the shower.
Here is my question: does it matter if the sink/shower tee is above or below the toilet tee in the stack? The vertical distance between the T's will be about 8", and it is considered to be a wet vent for that 8".
Thanks in advance for your advice.