Reduce space of page

Hello,

I'm using the Fixed widget plugin for my site. It's working well but not with page with less content. e.g. this page

Because i have set margin-bottom for this plugin is 1300px so maybe this is the reason we have the space at bottom of page with the page has less content. With the page has long content, it's fine.

Please advice. You can use grant access for closer look.

Thank you,
Tuan.