I have the following simple Powershell script:
ii E:\\Source\\Development\\websites\\example.com.au\\root
ii E:\\Source\\Development\\websites\\example.com.a
You can use start-process instead of invoke-item, which will give you control of the window size. You can implement that with miminmal changes to the script by creating an ii function to override the alias temporarily, and then remove it when you're done:
function ii { start-process explorer -WindowStyle Maximized -ArgumentList $args[0] }
ii E:\Source\Development\websites\example.com.au\root
ii E:\Source\Development\websites\example.com.au
ii E:\Source\Development\websites\example.com.au\css
ii E:\Source\Development\websites\example.com.au\database
ii E:\Source\Development\websites\example.com.au\js
Remove-Item function:ii