The "drop-in backers" type of foam will buckle the vinyl because most are made of ESP- low density (1/2#) which really moves as it holds the moisture to expand/contract under the vinyl.
#6 here;
http://www.doityourself.com/forum/i...ers/49787-vinyl-siding-over-styrofoam-ok.html
Perhaps that is what you heard?
Your local code may require 1-1/2" in to solid wood or just 3/4" in to strapping, check with local AHJ. The older IBC required it. 1-1/2" is generally max. thickness (before strapping) because the foam will compress when nailing (hanging) the vinyl and prevent the required expansion/contraction inherent with that product due to temperature changes. Then it will buckle for sure, imperative to hang it on the wall, no tight (touching) nails;
https://www.vinylsiding.org/wp-cont..._Vinyl_Siding_Installation_Manual_English.pdf This could be the reason you heard about as well, without the backer board, just flat panels. The foam panels move as well, offset the joints with multiple panel, use a WRB over the taped joints/panels. Ask AHJ locally, for best installation.
FYI, the required max. nail shank size for vinyl (pp14) is 1/8" (0.125") shank per manufacturer's link, the 10d (3") shank is a little thicker- (0.1350") so it might void the installation warranty if ever a problem- possible buckling due to nail sides restricting movement in slots... something to think about.
Gary
