>> radiation beneath a ≈ 1.7 mm thick lawn of the melanized radiotrophic fungus (180° protection radius) was 2.17±0.35% lower as compared to the negative control.

2% doesn't seem much but again its just from 1.7 mm thick fungus. Wouldn't it be easier to grow it on Earth instead and test with thicker fungus layer for a significant attenuation of the radiation? I understand that they want to use it eventually on the ISS but couldn't the prototype be tested on Earth as well?

And for a layman digestible version https://www.scientificamerican.com/article/radiation-helps-f... (from 2007)