How much power does a K40 realy have?

I ever wanted to know how much beam power my K40 realy has. So I bought a Laser Power Meter from Cloudray:

There is not enough space to place the meter between the tube and the first mirror, so I measured after the first mirror. At 18mA the meter shows around 28W. I expected to be less than the advertized 40W, but 28W is a bit low.

Does anyone have such measurements for his K40?

When I replaced my tube I got a SPT tube from Lightobjects. They provided paperwork that said the tube was tested prior to shipping and had an output of 38W at a current of 16mA and at a distance of 24in.

I guess my tube is already degraded a bit.
It’s still the stock tube an I have operated it a few times over 25°C.