When resizing the interface the webpage you gets resized as well. So, for example, if you make the interface display @ 75% then your webpage will be 25% smaller smaller than it will be in ‘real life’ (in your browser). This is true even if the page size is set to 100%. The only way to see the true size of your page with a resized interface is to increase the zoom size by the same amount you decreased the interface size. So if you set the interface to 75% then you would have to set the zoom to 125% so see the proper page size.
This seems wrong to me. Setting the interface size should only size the interface, not the webpage.