Pixels to dips, desktop and android

I am using Libgdx to code an android game and as you may know, many screen resolutions cause some problems if done incorrectly. So I am trying to use this DP unit rather than pixels.

However, I have this method here:

public static float pixelToDP(float dp){
    return dp * Gdx.graphics.getDensity();
}

the Gdx.graphics.getDensity() method actually gets the SCALE, so it's already done for me.

Now the problem, libgdx is cross platform which is good for testing. When I launch this on my S4 which has a resolution of 1920x1080 with a dpi of a whopping 480, opposed to my terrible and overpriced laptop which has 1366x768 @ 92dpi it is placed exactly where I want it. On desktop it is way off, a good few hundred pixels on the X and Y axis.

Is this due to the fact my screen dpi is measured @92dpi, the resolution is a lot lower and the actual game is not fullscreen on the desktop?

Here is the code for drawing the object:

table.setPosition(MathHelper.pixelToDP(150), MathHelper.pixelToDP(200));

In order to get it perfect on desktop I have to do:

table.setPosition(MathHelper.pixelToDP(480), MathHelper.pixelToDP(700));

Which is not even visible on my phone, since the scale is actually 3x, which puts it a good 200 pixels off the screen on the Y axis.

Is there a way around this? Or am I basically going to have to deal with doing platform checks and different blocks of code?

Possible solution:

So I changed my dp conversion method, if I was to do 100 * 0.5 it would return a new value of 50 but in reality I want the orignal value of 100 + 100 * 0.5.

Not sure if this is a proper fix or not but regardless by table is drew in the exact same place on both laptop and phone:

public static float pixelToDP(float dp){
    if(Gdx.graphics.getDensity() < 1)
        return dp + dp * Gdx.graphics.getDensity();
    return dp * Gdx.graphics.getDensity();

Is this just a cheap fix or is this pretty much how it should be done?