I wish I had a good tip for you here. Which turnips are you trying to sow? Hakurais have worked pretty well for us in the turnip plate, but if they are slightly larger turnip seeds, I would maybe recommend either the radish plate or the light carrot plate?
As soon as you can afford it, invest in a Jang seeder and those small seed woes will go away. Accuracy of seed singulation will also improve. There is a learning curve: which roller to use (there are many choices); which gear combination to use? Experiment and keep good records of your settings and it will soon work out. Also, for around $125, you can get a double-disc opener to replace the shoe that comes with the stock machine, which works really well in the residue-rich surface conditions that no- or reduced-tillers encounter.
I am planting hakureis today, gonna try out filling the hopper more. Have you done the pvc cap adjustment Jesse?
I would love a Jang, I want to hold off for a few years if I can make the earthway work