i need to wireframe a concept for a responsive website. wireframe should demonstrate how the homepage's grid is going to look like on Mobile, Tablet and Desktop. i use Omnigraffle and have downloaded a stencil based on the Less Framework grid system (http://lessframework.com/). stencil can be seen here: http://www.graffletopia.com/stencils/745
now, my question is, when i import e.g. iPad/iPhone stencil objects to my canvas in Omnigraffle, how big should they be in order to maintain the correct proportions and fit the responsive grid layout?