got it - if Johnny’s has done the research I’d use that for your initial set-up, but know that you will definitely have to play around with the roller brush height to get the right spacing.
I usually end up seeding 1.5-2x the amount of seed I want to germinate and grow well. If calibrating the seed to singulate causes the seeder to skip over too many holes when you’re seeding, then I would either loosen the brush or use a larger hole size and distribute twice the amount of seed at half the rate (2 seeds every 6" vs 1 seed every 3").
lastly, if you’re not positive about using the jang seeder or how long you intend to grow sunflowers this way, I’d recommend buying the single jang and doing 3 passes. Yes slightly more time, but less expensive if you decide to go different route in the future.