Different regs for small subdivisions are a slippery slope into real problems. Folks doing three lots, or six, or nine have exemptions in many many places, (not always total exemptions) and the result is that landowners create almost unending problems affecting access, services provision, stream corridors, etc. without any significant review. This is also drastically unfair to larger landowners, who are saddled with all sorts of requirements. If your state does not tie your hands, you should review every lot split under, say, 160 acres, and add a requirement to your regulations that you will not approve any land divisions without seeing a plan for the owner's entire contiguous holdings!