Hi Rico, 

Thanks for reaching out to us. 

You can use some CSS to change the value of the opacity but it will have an effect on the functionality of the hover. 

Try this out to see it: 

.portfolio-items div.work-info-bg {
    opacity: 0.2 !important;
}

There isn't an option for this otherwise, you may need to edit the theme files to get this done. 

Let me know how you get on. 

Cheers