The presentation gets the size from the layout manager

bigbluebutton-html5/imports/startup/client/base.jsx

...ton-html5/imports/ui/components/actions-bar/component.jsx

bigbluebutton-html5/imports/ui/components/app/component.jsx

bigbluebutton-html5/imports/ui/components/layout/context.jsx

...ton-html5/imports/ui/components/layout/layout-manager.jsx

.../ui/components/media/webcam-draggable-overlay/context.jsx

...ebutton-html5/imports/ui/components/nav-bar/component.jsx

...luebutton-html5/imports/ui/components/nav-bar/styles.scss

...n-html5/imports/ui/components/panel-manager/component.jsx

...on-html5/imports/ui/components/presentation/component.jsx

bigbluebutton-html5/private/config/settings.yml