I was looking around for something like this, and this mod seems to be the best fit for what I was looking for.

But I am wondering why you settled for 4x?

I ask because in vanilla I find it extremely weird that a cargo wagon holds less stuff (40 stacks) than a single steel chest (48 stacks) when the wagon's footprint is 6x that of a chest. To my mind it would need to hold at least 288 stacks (6 x 48) to make sense, which is 7.2 chests. An 8x multiplier seems more reasonable to my mind.

Thanks for your feedback! Scales in Factorio are somewhat odd, a lot of the decisions revolve around balance. I'm not complaining I can hold 3 trains and a handful of oil-refineries in my backpocket :)

If you think about it, cargo wagons are much higher than a chest too, so factor 16 seems most realistic... OR teeny tiny steel chests simply have too much storage space. Having said that, I could make the cargo wagon capacity multiplier a setting, but beware that if you switch from larger to smaller, you may lose a lot :)

If you feel adventurous, extract the zip-file of the mod, open data.lua (with any text-editor) and change the value on line 3:

• local storageMultiplier = 4;

to any value you like! It's really that simple :)