Page.modular don't work as expected

Hello! I want to modify a base.html.twig template, so it will have a little difference when rendering modular pages. However, page.modular returns false in base.html.twig template and returns true only in modular block templates, where it should always return true. Is it a bug with page.modular() function?

page.template == 'modular' works like I want :)