Thanks for reaching out and thanks for using the Monument WordPress theme with BoldGrid Post and Page Builder for WordPress! Sorry to hear you’re having issues with your header menu placement.
The main issue is with the Monument theme itself, “Monument” is considered one of our legacy themes so at this point it is no longer maintained to stay up to date with WordPress’s latest standards. I replicated your issue and I see exactly what you mean. One thing I would suggest is maybe combining some of your menu items into sub-menu items to free up more space in the page header. That way you can free up space at the bottom of your “sidebar nav”.
Our legacy themes have all been replaced with our flagship theme Crio Pro WordPress Theme. With Crio you’d have the ability to create custom page headers and with its over 400 customization options could build your ideal header in a theme that is very well maintained and supported.
I hope this helps. Please let us know if you have any other questions.