What ratio to mix lawn fertilizer with ammonium sulfate?

I would like to know if anyone has experience mixing fertilizers. I have a small hand held broadcast fertilizer spreader and wanted to know at what ratio to mix the fertilizer in it when i apply. I have Schultz Super 21-0-0 ammonium sulfate with coated urea and also primarily use Scotts Turf Builder With PLUS 2 Weed Control 28-1-4. I like the effects of the Schultz quick ability to green up the lawn and also the weed control and results I get from Scotts. I fertilize about once a month and have primarily used the Scotts but wanted to mix in the Schultz. I have read some articles of people who just follow up a balanced lawn fertilizer with a 21-0-0 ammonium sulfate but it seems like that would be too much Nitrogen since Scotts carries a 28-1-4. Thanks for the helpful advice.