Anyone every planted sunflowers with their drill - closing up the holes to get a row every 28”. I have a woods seeder - and it will not go down to 15 lbs per acre sunflowers without closing up some of the holes. Not talking about a seed mix - straight sumflowers
Probably 22.5”. The fewer rows, the wider the openings. My woods seeder tends to chew up sunflower seeds when you are seeding more rows but the seed openings are small. The fewer the rows, the larger the openings. I have read some grain drills have the same problem.