It's weird but a lot of fanfics have the percentages be really weird too, asking if in the next 7 days Coil will use a precog power shouldn't give an answer like 83%, Coil uses his power constantly because he's a control freak, even when he doesn't look to be using his power he's using it to play out different wording to statements, learn things he couldn't otherwise, steal info from the PRT without a way to trace it, etc.

To say there's a 17% chance of him not using his power implies that even with him constantly abusing his power he's got a 17% chance of getting in a situation where he can't use his power in the next week before he next uses it(dead, coma, trapped in master/stranger protocols, etc). 17% is a stupidly high chance for any of those things to happen in the next 10 hours at best(assuming he goes home and sleeps for 8 hours and doesn't collapse the timeline and make a new one before the next morning giving him 2 hours for getting home and to bed, which feels fairly generous for someone who's trying to maximise their gain from their power).