You can purchase a small part for your loupe that will allow you to shift the barrel downwards and increase the declination angle as well.

The loupe on the left has this plastic part installed and therefore has an increased declination angle
as compared to the loupe on the right which does not have this part installed.

The mechanism allows you to lower the barrels as well

Here is a video showing how to install the declination angle  enhancement part onto your loupes: