Hello,
On the latest build (8A21, Intel, macOS 11.2.1), SD8 does not appear to respect the default window size (set from the Window menu), either on launch or when creating a new window.
I’ve tried resetting the default window state & size, and using both unsaved & saved scripts in order to set the default window size, with no success.
Came here for the same issue, two years later.
Is this fixable? Makes me insane.
Edit: Using version 8.0.5 of Script Debugger on m1 Mac mini running macOS 13.2.1 (22D68) Is that info the key to getting this fixed? 
I’ve currently remapped ⌘⇧-N to a Keyboard Maestro macro that opens a new default script template, enables the Event log, resizes to preferred size. But I totally shouldn’t have to, no?
We have addressed this issue in the Script Debugger 8.0.6 8A66 prerelease build. if this problem persists with this build, please let us know here.