My suggestion is just keep trying. You should check your inventory and tinker's workbench after every major scrapping session. It's easy to miss the left side notification popup alerting you to either getting a mod or learning how to craft the mod. My best guess on my personal results are...that I've scrapped near 1000 items. And the results were 11 learned mods [5×*, 5x** and only 1x***] along with around 10 ready to use mods. About half both i probably won't use but the others are what i wanted. Keep trying and remember to scrip any items you don't want to learn or get the mods for.
