Ten was a Heavenly Number, and in this case, for Spiritual Sense a hundred kilometers was the limit. When Di Tou unfurled his Spiritual Sense three times, it extended ninety-nine kilometers and nine hundred ninety-nine meters. If he were to add his Void Qi, he could add the last meter with 'nothing.' Making it both one hundred meters, and not one hundred meters, skirting the rules.
Di Tou had only done this once in his life, and that was when he had been answering questions on the Selfless Pavilion's trial grounds, and that time, thankfully, he hadn't managed to attract too much attention due to the strange nature of his 'extension' where he surpassed, but also didn't fully surpass the Heavenly Limit.
In terms of distance, this one meter couldn't be considered much, and was pretty much irrelevant.
