I've used flood-cheks on three installations: two TL's and one FL. All installations had goose-neck 45 fittings. (I would not install washer hoses anywhere without them. They relieve stress at connection as well as saving machine-wall spacing.)

My installs all had in-the-wall water supply and drainage fittings with the water-supply openings flush with the wall. The drain-hose from the machines to the wall-drain required a bigger gap than the the hoses so supply-hose space didn't even have to be considered. The machine-to-wall gap required to accommodate that drain-hose loop is about 4".

If your drain-hose goes to a sink and doesn't take that kind of space behind your machine, 3" will still leave enough "jiggle-room" for the flood-check hoses to dangle freely. (assuming you use 90-elbows or 45-goosenecks.) If your supply-spigots protrude from your wall, you may have to allow more.

If you have opportunity of recessing your supply connection points further into the wall, maybe you can close the gap further. The hoses themselves are about 7/8" OD along the length. About 1 1/4" at the fitting-ends.