Thought maybe the multiplier between Nameless Namek (20,000-200,000, depending on if Guru meant Nameless could compete with Base Vegeta or Ozaru Vegeta) and Kamiccolo (1,000,000,000ish) could be the same as between post-split young Piccolo Daimao (300ish) and Android Saga Piccolo (360,000,000ish), but tried it and it doesn't work at all. One is like x4000-x40,000 and the other is at least a million.
Idea was that the fused version could've powered up by the same multiplier that the unfused Piccolo did. Can't think of another way of having a non-random multiplier.
Piccolo divided by kami and then multiplied by a constant number doesn't work either, since for Nameless the constant would be between 200,000 and 20,000 (20,000-200,000 divided by 300/300 (which is = 1)) and for Kamiccolo it would be about 700 (1,000,000,000 divided by (360,000,000/250) is 694).
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Only other way that kinda works if you only divide Piccolo by Kami when they have an actual gap between each other. Then, assuming Guru believed Nameless would have been able to compete with Ozaru Vegeta and therefore probably had a PL around 200,000, Nameless would be 650 times stronger than a young Piccolo Daimao (300 PL). Then for Kamiccolo, because there's an actual gap between Piccolo and Kami, you divide the stronger's PL by the weaker's, which in this case is about 360,000,000/250, which is 1,440,000 and then times the multiplier of around 650, which gives 936,000,000, which is around 1 billion, which is about where I'd put Kamiccolo. Here I'm assuming there was never much of a gap between young Kami and young Piccolo Daimao. Even if the PLs were a little off, it could still work. For example, you could have Kamiccolo as low as 800,000,000 and still it would work, if you increase young Daimao's PL to 360 (200,000/360=555, then 1,440,000x555=799,200,000, which is about 8 billion).
(Got the 1 billionish for Kamiccolo from Mecha Freeza being around Namek Goku's 150,000,000, Trunks being x2 that (so 300,000,000), Goku and Piccolo Android Saga being 1.2x Trunks (360,000,000), Vegeta being 1.5x Trunks (450,000,000), A18 being x2 that (900,000,000) and Kamiccolo being a bit above that)