Open the bindings panel, and expand the WA UPloaded Files (file Field Name) Binding group.
This binding group contains all the bindings for details about the uploaded image including server file name.
if you look carefully, you will see that the there is an initial group of bindings, then they repeat but preceded with the upload folder. The bindings preceded with "images/detail/" are information unique to the file created in the details folder.
the bindings preceded with "images/thumbs/" are unique to the file created in the thumbs directory.
to store the thumbnail name, use the server file name binding that is preceded with the images/thumbs/ folder name in the insert record behavior.
The image height and other setting should also be using the bindings from the WA UPloaded Files (file Field Name) Binding group