returns the face of an object that was clicked on ?

Possible applications : bullet holes in walls/ parts, melee weapon marks, blood spills on walls. If I get this part right, it should be easy to attach a GUI with an ImageLabel on the clicked face, at the approximate position of the mouse hit.

The following code goes inside a LocalScript. Problem is, it only gives the right answer part of the time (about half of the time it returns the wrong face). How can I make it more accurate, please ? Thank you.

local Player = game.Players.LocalPlayer
local mouse = Player:GetMouse()


for i = 1, 20 do    -- generating 20 random parts   
    local part = Instance.new("Part", game.Workspace)
    part.Name = 'random part'
    part.Anchored = true        
    part.Size = Vector3.new(math.random(1, 20), math.random(1, 10), math.random(1, 20))    
    part.Position = Vector3.new(math.random(-50, 50), 5, math.random(-50, 50))
    part.BrickColor = BrickColor.Random()
end

mouse.Button1Down:Connect(function()    
    if mouse.Target then
        local hitPos = mouse.Hit.p 
        local hit = mouse.Target -- object that was clicked on      
        local sides = {}
        local sizes = Vector3.new(hit.Size.X,hit.Size.Y,hit.Size.Z)
        local pos = hit.Position -- [vector3 of] position of the object that was clicked        
        sides[1] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(0,0,-hit.Size.Z/2))  --front
        sides[2] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(0,0,hit.Size.Z/2))   --back
        sides[3] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(hit.Size.X/2,0,0))   --right
        sides[4] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(-hit.Size.X/2,0,0))  --left
        sides[5] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(0,hit.Size.Y/2,0))   --top
        sides[6] = pos + hit.CFrame:VectorToWorldSpace(Vector3.new(0,-hit.Size.Y/2,0))  --bottom

        local ClosestSide = 1
        for i,v in ipairs (sides) do            
            if (hitPos - v).Magnitude < (hitPos - sides[ClosestSide]).Magnitude then
                ClosestSide = i                     
            end
        end

        print ('ClosestSide is : '.. tostring(ClosestSide))     

        if ClosestSide == 1 then print("front")         
        elseif ClosestSide == 2 then print("back")              
        elseif ClosestSide == 3 then print("right")
        elseif ClosestSide == 4 then print("left")
        elseif ClosestSide == 5 then print("top")
        elseif ClosestSide == 6 then print("bottom")
        end

    end
end)