Port Perk - How does it work?

[Nurri 28]

So everyone keeps saying with the ports perk you should do 24hr ships. The 24hr offers a 20% success chance with a 260% yield. My question is regarding how exactly the % increase from the perk works. It says it has a 20% increased return rate and +15% more rewards. If I understand this correctly that means a 20% increase in the return rate aka the 24hr option goes up to 24% and a 15% flat increase to the yield aka 275% yield then. This is how it makes sense for me but then why does everyone say the perk massively changes whether you should do the 24hrs option or not? Am I doing a mistake here and in reality with the perk the return rate goes up to 40% and the yield to 299%?

I've always assumed that I read it wrong and it is a 20% flat increase added to the current return rate, so it goes up to 40% and not only to 24% but now that I've tried a 2hr ship which has an 80% success chance and I've had one not returning from that I'm rethinking it since with a flat 20% increase it'd be at 100% and couldn't fail.

Edited October 15, 2018 by Nurri

[Chloe 33]

I think the percentages are flat, so you'd get a flat 20% boost to your return rate on ships. Making 24h ships 40% successful. Over time, that would mean 24h is the most profitable choice for sending out ships. Personally I prefer 12h for some reason. Not fond of all my ships failing I guess.