Mine have been in clay soil for years so don't get any wider than two feet across. I have drainage problems too but they thrive somehow. I use mine as a border against a shed. Have six in a row and they do fine besides the occassional flattening by the groundhog.

I have one in a flower bed with Agastache and other perennials like Echinaceas, Coreopsis, and Hesperaloe 'Brakelights'. It is a nice contrast for purples and reds. Ornamental Grasses and Roses look good with it too.

I also have 3 in big urn planters with Sedums and Delospermas around them. They don't get 4 feet wide unless you let the offshoot pups stay and grow there. I usually separate mine and put them in other places. They root and separate really easily.