Yes, I know IE11 is a dinosaur. But I have to provide *some* support nonetheless.
In IE11 only: I have an image/ad unit in the generate_hook_before_main_content slot that extends all the way to the right of the page, underneath the generate_before_right_sidebar_content hook in my right sidebar.
Any attributes you can suggest to get the main_content hook to align with the main content container?
All hooks have a default priority of 10. The lower the priority, the earlier the hook fires.
In this case, our columns container for the blog is hooked in using the 10 priority, so by defining a lower priority for your Hook, it makes it so the element displays before the columns container.