Yeh you are right, opening the .ini file you can tweak the background configuration but I suggest to try first different themes as every skinner use different settings and you can find the one fitting your needs
aw the space between the icons\objects depends on the icon size not every skinner set this parameter so if you open the .ini file and you don't find any referee to [Tile] you have to add the following lines:
[Tile]
Image = Docktile.png
ResizeIconByPercent = 95;
OffsetIconByPercentX = 50;
OffsetIconByPercentY = 50;
moreover you need (in the same .ini file folder) a transparent .png named Docktile.png, to have more space just decrease the size to 90\85\...
btw embedded in my last skin "WhiteCristmas Docks" you can find a transparent .png ready to be copied ans used
reuploaded here https://www.wincustomize.com/explore/objectdock_backgrounds/289/
let me know !