Because it's parboiled... does that mean it's ready for the mash? Occasionally I'm not sure about what is mash ready and what is not. I have never done a cereal mash. I'm not sure why something like masa harina is ready for the mash... what process did it go through to get there? Same for me with rice. The only rice I've used in homebrewing was flaked rice and that was way back in the mid-50s.
There's a better chart out there than this but........
and of course wiki
httpss://en.wikipedia.org/wiki/Starch_gelatinization
Simply put starch needs to be freely available for amylase to chew it up. Heat usually does this. I've yet to see an explanation of why a cereal mash needs to be done. Cook up your adjunct to gelatinization temps in small enough pieces and throw it in the mash. Of course with enough DP in the rest of the mash to convert. Flaked adjuncts are heated up to gelatinization temps from the speed they go through the rollers. A lot of starch adjuncts will be fine simply with mash temps given enough time.
I just like to play with stuff. Sweet potatoes can be mashed. They already have amylase available and will convert fine by themselves. A friend and I made an English Pale Ale with them for grins. Not much came through - good since I don't like sweet potatoes.