rk-wilde33 on "Image centering when using "viewer_size_image"-plugin"

Hello,
I'm new here and not experienced at all. Didn't find my issue here or anywhere else.
Using theme "default / sterile-light" and plug-in "viewer_size_image" I found this behaviour when displaying single pics: pics in landscape orientation center automatically in "595-995 px" - size, pics in portrait orientation center automatically only in "995 px" -size.
Pics in smaller sizes than specified above get displayed in different positions leaning to the right of the display box.
Is there an oppotunity to get all displayed pic sizes centered automatically? Where and how to "tune" the pic's position?
Thanks!! in advance.
rk-wilde33