forgive me if this is too simple of a question but here it goes: What is the pathname of my texture I use for my custom city profile ?

I have an image i want to use as the icon. Ive tried putting the image in the mainmenu folder, and setting icon=mainmenu:myimage.png it doesnt work
icon=/resources/mainmenu/myimage.png it doesnt work
icon=$lostcities/myimage.png it doesnt work (which would be lostcities/configs/myimage.png)
icon=myimage.png and put image in the root folder (.minecraft/mymodpack/)

so what should the pathname/filename be?