Using weights for bluefin

[CHANCE1234]

Guys, whenever I go bluefin fishing I usually just sent the baits below the ballon at varying depths and assume they stay there. Obviously using weights would guarantee the baits stay at the proper depth so a few questions:

If I'm marking fish at say 80' do I set me weight at 80 feet?

If I do the above how far from my bait do I set my sinker?

Thanks for any help.