wire dia : #18 ga or so is fine ..
Nothing is exact .. or perhaps reworded
” It is impractical to attempt to derive an equation for the electrical properties of Every possible fraction of a mm of every component “..
Or by the time you build a valid NEC model to do so ( and Tested ), you may find interest in a new hobby.
Make estimates, build, and use equipment to finalize.
That’s why ‘Textbook’ info does not match Reality.
AND :
Everything Interacts = the installed Fn may be a bit lower than what you obtain with the feed Unmounted
I typically tune the loop antenna to 1440 MHz before installation in the 6-inch cake pan to have it @ 1420 MHz installed.
Alex Pettit