Need help splitting into prime numbers

[Hammerhead]

Okay, so I've been using complex splitter arrays and loops to split off exact fractions from my main belt. For example, early on I had 4 belts of iron on my main bus, and I needed 5/16 of my total iron production split off to feed my green and red science. So, I split one belt into 4, and then had one of those quarter belts and another full belt diverge off into my science manufacturing area while rebalancing the others back down to 4 belts again. I've been able to manage more complex fractions too, from 2/15 to 5/96. However, I'm currently at a point where I need 5/364 of my copper production and 20/143 of my iron production to perfectly supply a part of my factory. These numbers factor down to 5/(2*2*7*13) and 20/(11*13). Now, I can manage to split off 1/7, 1/11, or 1/13, and I could use these methods in tandem by, for example, splitting a belt carrying 1/11th of my total production into 13 parts, and thereby manage to get 1/143 of my production on a belt. However, my methods for doing this are a little on the sprawling side, and compounding two of my prime-number splitter arrays like that will eat up space like no one's business.

I was wondering if anyone had any space saving tips for designing splitter arrays or any example splitter setups that I could look at and get ideas from.