Why does phrase pump give me sentences with so many unknown words?

I love the idea of phrase pump but I’m having a lot of difficulty with it so far. It feeds me sentences with a lot of words that I don’t know. At first, I thought maybe this was due to the fact that I wasn’t marking enough words as known, learning, etc. But I’ve now marked a lot of words and it’s still giving me sentences with lots of words that I don’t know. In theory, the sentences should be composed of at least 80% known words, right? That’s generally what you need for comprehensible input, right? Anyway, I really wanna use this tool. In theory, it would be realllly helpful. Is there anything that can be done so that it feeds me sentences with fewer unknown words?