Low boost reading E300td
 

I've just installed a boost gauge and I think im getting a low reading compared to what Ive seen on the forum. Ive installed a boost gauge in the line between the intake manifold and the boost/map sensor.
The highest reading I've got is 0.6bar max, normally 0.5bar.

Is this right or is the problem to do with where I have tee'd in the gauge, ive check the hoses and there is no visible leaks.

I also have the 12k resistor mod installed to give a little extra boost which isn't helping.

Any ideas what could be wrong