Ahh, well I'm not sure then. What if you add the height into both the div and the ins? Sorry, I just haven't messed with it in a while. The way I posted is how all my ads are and it's worked for me for years now on both desktop and mobile devices.
The only problem I've noticed is if someone loads the page in a wide screen, then tilts their device back to narrow, the div will stretch beyond the page. As soon as the page is either refreshed, or changed, though, it's fine again. I assume this probably doesn't happen enough for it to be an issue so I've just left it as acceptable.