Generate perfect box Region3?

Alright I'm trying to generate a box that's 80,40,80 in a region 3 but I get odd sized boxes like 80,40.4,79. Things like that.

This was for a mini map and I wanted to generate a little square of: http://prntscr.com/9gy9q8

Local script in a gui:

function createRegion3(startp, endp, num)
	local region = Region3.new(startp,endp)
	local part = Instance.new("Part",game.Workspace)
	part.Anchored = true
	part.Size = region.Size
	part.CFrame = region.CFrame
	
	for _,Part in pairs(game.Workspace:FindPartsInRegion3(region,nil,100)) do
		print(Part.Name)
	end
end

--x,y
while wait(5) do
	local pos = game.Players.LocalPlayer.Character.Torso.Position
	createRegion3(Vector3.new(pos.X-40,pos.Y-20,pos.Z+40),Vector3.new(pos.X+40,pos.Y+20,pos.Y+40),5)--B2
	print('getting region 3')
end

The region itself is the correct size (you can check by printing it).

The problem is that when you set the .Size on a part, it first consults the part's FormFactor property. The FormFactor tells the part how to round the size out.

If you want to have arbitrarily sized regions, you have to set part.FormFactor = "Custom" before setting the size.

Note that you can't set any dimension to be smaller than 0.2, even with Custom FormFactor.