I have the following convention for most of my projects:
/src /Solution.sln /SolutionFolder /Project1 /Project2 /etc.. /lib
The most consistent way is by using nuget config to explicitly set the config:
nuget config
nuget config -set repositoryPath=c:\packages -configfile c:\my.config
https://docs.microsoft.com/en-us/nuget/consume-packages/configuring-nuget-behavior#changing-config-settings