Dear John,
Thank you for your suggestion. I will have a look into the Pro version. The other options were known and tried, and of course they are working, but I prefer to have it realised by using that close button on the active window (which happens to be resized and moved frequently). Otherwise I have to remember that in this specific window/program I have to use the titlebar (or a shortkey which I tend to forget too). And if I accidently want to move that window, it closes. I like to keep it simple. The close button it is.
But thank you for your advise.
A.Zwaan