Adjust width of spacer between Mac OS dock icons

Many of you might know that it is possible to add a spacer to the Mac OS dock icons with:

$ defaults write com.apple.dock persistent-apps -array-add '{"tile-type"="spacer-tile";}'
$ killall Dock

but the problem is, I find them a bit wide. I'm wondering if anyone knows a way to adjust the space of those spacers

An image of the spacers I'm talking about can be found here

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