Part doesn't move to side/top of part surface side?

    local Players = game:GetService("Players")
local player = Players.LocalPlayer
local mouse = player:GetMouse()
-- Check that there exists a part at which the mouse is pointing
while wait(.5) do
	if mouse.Target then
		print("The mouse is pointing to the " .. mouse.TargetSurface.Name .. " side of " .. mouse.Target.Name)
		local focus = mouse.Target
		local PartSize = 4
		local deltaz, deltax, deltay = 2,2,2
--		if mouse.TargetSurface.Name == "Top" then
--			deltaz, deltax, deltay = 0,PartSize,0
--		elseif mouse.TargetSurface.Name == "Bottom" then
--			deltaz, deltax, deltay = 0,-(PartSize),0
--		elseif mouse.TargetSurface.Name == "Left" then
--			deltaz, deltax, deltay = PartSize,0,0
--		elseif mouse.TargetSurface.Name == "Right" then
--			deltaz, deltax, deltay = 0,-(PartSize),0
--		elseif mouse.TargetSurface.Name == "Front" then
--			deltaz, deltax, deltay = 0,0,PartSize
--		elseif mouse.TargetSurface.Name == "Back" then
--			deltaz, deltax, deltay = 0,0,-(PartSize)
--		end
		local pos = focus.Position + (Vector3.FromNormalId(Enum.NormalId.Front)*deltaz) +(Vector3.FromNormalId(Enum.NormalId.Right)*deltax)+(Vector3.FromNormalId(Enum.NormalId.Top)*deltay)
		print(pos)
--		if pos.X > 4 or pos.Y > 4 or pos.Z > 4 then
--			pos = Vector3.new(0,0,0)
--		end
		game.Workspace.Grass.Position = pos
	else
		print("The mouse is not pointing at anything.")
	end
end

I'm trying to move the part to the correct side of the other part based on mouse.TargetSurface but instead it does this:(https://gyazo.com/217feb4a923d2c52b3fc6163bc08b060) The parts are 4x4x4