It appears the new anti-stacking fence foundations has a bug where you can get (free-handly) about 1/2 the density that you used to have before.
I found I could get (at least) as close as my 2 sandstone fence foundations here free hand, until I was attacked and dealt with a shoebill that interrupted my testing. Then the game would no longer allow me to place parallel within 1 foundation square.
I had seen someone online testing it (and yes, for test live) and they were getting closer than I had thought possible, but it appears the Devs have only sort of implemented this so far.