Radiation formula (per turn?) with no rad armor is rng(0, radiation/16). This rounds down to 0 for values lower than 16.
As a result, lightly irradiated areas like (some?) craters are completely harmless and minor radioactivity mutation does nothing (except raising player temperature, annoying geiger and intimidating the player with possibility of it mutating into full radioactivity). Areas above 15 are impossible to craft in or sleep in without protection (even with iodine and radiogenic), which makes non-minor radioactive mutation totally unbearable to anyone without a cleansuit or something better.
For cleansuit, the formula is rng(0, radiation/40), which covers entire ground level hazardous sarcophagus and full radioactivity mutation. As long as you wear your cleansuit, the waste sarcophagus is a safe place to sleep in.
The fix is trivial, but maybe it’s all intended.
For example, at the moment minor radioactivity isn’t unbearable, while with a naive fix (x_in_y(division remainder, 16 or 40) chance of gaining a rad) it would overpower both iodine and radiogenic, forcing the survivor to sleep and craft either in cleansuit, radiogenic AND with iodine or just in full hazmat.