I'm close to that same ratio. I'll use that amount to drop my MF medium to soft. If I'm adding salt or glass beading or even floating additive, I adjust from there. I'll even add softener to the soft blends when using additives. As far as using the same brand softener in like brand plastic, I wouldn't worry too much. I've been mixing and matching for years without issue. I don't want to keep buying more softener every time a manufacturer changes formula for their plastisol, and I change brands. I just use what I have whatever I have on hand. Example- I have almost exclusively used MF plastisol. But I can't get it anymore. I had also tried Dead On, and bought their softener to go with it. When I was able to get MF again, I just used Dead On Softener in my MF. No problems. Same with Bait Plastics. I used either MF or Do It brand of softener, no issues then either. Now I can't get MF again But still have at least a quart of Dead On softener. Don't know what platic I'll get to replace the MF, but I won't spend$$ for new softener. Same with Hardener. I've tried them all. I have LureCraft. I hate it because of the color and smell, so I tried Do It Crystal Clear. Worked fine in whatever plastic I was using. Others may have had different results. This is only my experience. Best I can tell you is, experiment And have fun.