I mixed hard small heavy seed in the small seed box in back. Obviously fluffies in native box. If there's "light" non fluffies, I'll mix in the native box as well. Canadian rye I put in with fluffies. I suppose a guy could tweak the big seed box to accomodate stuff like canadian rye, etc. I probably wouldn't. "light weight" - put with fluffies. Heavy, go in small seed box. Just my opinion and 2 cents and how I do it. easy to adjust volume based on mix (some seeds bigger as you showed) on back of drill for lbs per acre. If it's bigger seed you're mixing in with some smaller stuff, look at ratios you'r mixing and then figure out how you want to set the dial on lbs per acre. So, if I'm wanting switch at 3 lbs to the acre & I have another set of seeds I want to be 7 lbs to acre, pretty easy to mix the ratio and set seeding rate with lever on back- if bigger seed, I may need to do a little guesswork to get it precise. I will manually make sure seed stays mixed in small seed box as well every couple acres. It usually is fine but of course, switch & similar have tendancy to go to bottom, but it's very minor and not bad. Little mixing by hand keeps it mixed well. good luck!