These responsive utility classes use viewport sizes as the determining factor and not specifically anything to do with the device.
You can see this here in the chart: http://dev.themeblvd.com/tutorial/responsive-utility-classes/
So basically, anything above 800px is not considered a “tablet” viewport size. When you’re viewing your iPad in landscape, I believe you’re viewing the site at a 1024px, which is the equivalent of a small laptop, and so you don’t really have any responsive elements taking effect.
Note: In the next theme update, this is changed from 800px up to 980px. This is not relevant to your question, but just wanted to note that here in case anyone is reading this later.
If you wanted to target the actual devices (opposed to viewport sizes), you could use the Widget Logic plugin and use
wp_is_mobile() in your widget logic fields of the widget.