Is the scale also smaller in the Z-axis, or just in the X and Y axes?
If it is smaller in all 3 axes, then go to Tools > Options, select the Models tab, and add an import action to scale every model you import to 94%. That way when it is printed, it will end up being 100%. They have a video about it here:
https://www.youtube.com/watch?v=E8ytvwfCn5g
If the problem is just in the X and Y axes, then you should try the horizontal size compensation. You can find that setting on the Other tab. For example, if you set to -0.1mm, it will shrink the entire part by that amount. You can read more about it here:
viewtopic.php?f=8&t=2042
And finally, one other suggestion - you should check to make sure you are not over-extruding as well. Because that can definitely cause incorrect size too
