The main issue is density, or the distance between rows, and here is where you get to make a decision. When a fill executes, it puts a lot of stitches into the fabric. Those stitches displace the fabric somewhat, just like when you get into a bathtub, the water has got to go somewhere – stitches in fabric are the same. So the more stitches you put into the fabric, the ‘bigger’ the fabric has to become to handle it.
Remember that density is measured in stitch points, which are tenths of a millimeter. The bigger the distance, the lower the density.
In the past, the typical production method was to use a cut-away stabilizer that can hold together with a lot of stitching in it, which relieved the fabric considerably. Then, the designer could use densities of 4 points or even tighter, thus creating “full coverage.” Full coverage means the fabric does not show through. It sounds good and if you’re being paid by the stitch, it is great. But what if you want the fabric relaxed, not stiff as a board? And full coverage isn’t as important as wearability and softness? Then plan on releasing some of the density. Go for 5 point density or even lower.
There are other options too. Using two fills, in different directions, but each with only half the density, you can create a far more stable fill with less displacement. And the coverage works out quite nicely.
If your fill sews out like a soup bowl, indented and firm, you needed less density and more stabilization.