I tried this topic before but got no takers.

I am a fan of Sly Arena and have read/studied his book "Speedlighter's Handbook"
and seen some of his classes at Kelby Training.

One question I can not find an answer to is:

When using canon off camera flash (580EXII) with an A and B channel, and using ETTL.
The preflash fires from the master and this calculates the correct/predicted best flash exposure.

When I use A and B. Assuming the ratio is set to 1:1.
Is 1/2 of the calculated flash exposure sent to A and 1/2 to B
or does each channel get a full dose?

What if I have multiple flashes set to B?

What if A is set to flash 'disable' and only fires the preflash?