How to set up pop-up window to open from the top of the page?

I’m making a portfolio website and used a really high pop-up window as a detail page for each project. And when I click the project thumbnail that is displayed on the bottom of the work page, the pop-up window doesn’t open from the top of the page so you can’t see if it’s open or not. How can I set up the pop-up window to open from the top of the page?