Created attachment 8323 screenshot showing buffer space Pygrid is a small program which allows you to configure window tiling and move programs to tile locations with hotkeys. It has a spacing value which controls the buffer space between tiles/programs. The default was 4 (units?); I've changed it to 0 but despite rebooting, catfish doesn't respect this and sizes to a 4 unit buffer regardless. Bug report on pygrid github here [https://github.com/pkkid/pygrid/issues/13] but crossposting as it's currently unclear which of the two programs is causing the issue. Thanks!
Since this issue is caused by client side decorations, I am marking it closed in favor of allowing the user to switch to the standard titlebar layout. From the following commit (available in the next release), you can now change switch to the classic layout to resolve this issue. https://git.xfce.org/apps/catfish/commit/?id=b0476823471bac6aef18acd4f05e3c86c4f6d48c Menu > Preferences > Appearance > Window Layout