Flow Settings in Cura 2.4 for Ultimaker 2+ not available (suspected overextrusion filling small holes)
For the Ultimaker 2 flow is typically handled on the printer.

You could make a feature request at github to let Flow be enabled for Ultimaker 2 printers.

As for your problem: that sounds more like a dimensional accuracy problem to me. I suggest setting Horizontal Expansion to -0.15mm.