Grid Alignment Errors - "for" loop

Goal: Align the transparent blocks (created by script) with the designated part.

Issue: Grid is off by some amount.

function GridModule.CreateGrid(MapModel, TestModeBool)
	if MapModel:IsA("Model") then
		print("The target map is a model! Attempting to run.")
		local MapSize = MapModel:GetExtentsSize()
		local XSize = MapSize.X/4
		local YSize = MapSize.Z/4
		local MapPivot = MapModel:GetPivot()
		print(MapPivot)
		print(XSize, YSize)
		for x = 1, XSize do
			for y = 1, YSize do
				local rayOrgin = Vector3.new(MapPivot.X / 2 + (x * 4), 400, MapPivot.Z / 2 + (y * 4)) --Issue is HERE.
				local rayDirection = Vector3.new(0, -450, 0)
				local rayParams = RaycastParams.new()
				rayParams.FilterType = Enum.RaycastFilterType.Blacklist
				rayParams.FilterDescendantsInstances = {MapModel:FindFirstChild("RayIgnore"):GetChildren()}
				
				local rayResult = workspace:Raycast(rayOrgin, rayDirection, rayParams)
				if rayResult then
					GridModule.GridData[x.."/"..y] = {rayResult.Position, false}
					if TestModeBool == true then
						local newPart = Instance.new("Part")
						newPart.Parent = workspace
						newPart.Position = rayResult.Position
						newPart.Size = Vector3.new(4,2,4)
						newPart.Anchored = true
						newPart.Transparency = .5
					end
				end
			end
		end
	else
		warn("WARNING: Attempted map is NOT a model!")
	end
end