Font size or DPI scaling dimension?

Hi,
I don't know if I'm in the correct forum, and I apoligize if I'm not, but it looks like I cannot scale properly some Qt applications I'm running.
For instance texstudio (a latex editor) start with a tremendously huge font size, such that I cannot use or change the editor at all.

My apporach to solve the problem is to set externally some parameters, such as the DPI scaling of the windows.
For this, I've played with the following parameters:
- QT_AUTO_SCREEN_SCALE_FACTOR
- QT_SCALE_FACTOR

But I haven't got any results so far. On top of it, setting a specific style (like GTK+ or a gnome default style .

I have installed the package qt-config (and qt5-qtconfiguration) using the dnf package manager of my fedora 26, but I'm unable to find anywhere an executable called qt-config.

Can you help me?

Thanks.