2 relay trans brake 6R80 - need input

[Stroke]

Hello, id like to know when you are doing 6R80 2 relay trans brake, people wire them to solenodi B and solenodi C which is B for C - 2nd gear B-3rd gear
my question is: why 2-3 gear solenoids when you are going to launch using 1st gear? or i am wrong and people launch in 2nd gear?

also when you do two relay trans brake, is there anything you need to adjust in tune to make it work?

thanks for input

[Onequiklx]

ive done the 2 relays on several cars. all it does is lock the trans down to where it wont move. most autos use rev/1st then releases rev when u release the transbrake. I will say on 1 car it did keep creeping on the transbrake. we never had to do anything to the tune to make them work.