iOS 100mb limit and installed applications question

So we all know the iOS AppStore 100mb limitation - you can download app via cellular only if it is under 100 mb size. Developers (me including) try and make miracles to keep their app size in this scope, but it is not that easy every time.
Yesterday I stumbled upon a game in the AppStore (made with unity personal edition as said by one of the splash screens) that in its description said it is 99,7MB, I was able to download it via cellular and started playing instantly (I assume no additional downloads were made when the game started itself). When I checked from my phone Storage settings it said the game was 300 mb… How is this possible? Is there a way to shrink 300 mb installed game to under 100mb…

As Hexagonious said, the installed size is likely to be much larger than the download size. In my experience, about 3 times larger isn’t unusual.

However, if the IPA produced from your game (before you submit to apple) is say 90Mb, then that’s not actually what your download size will be. For unity games, the app size is usually a whole lot bigger (maybe 30% bigger).

This is because apple will open up the IPA file, encrypt the contents (possibly minus the executable, I forget) and then put it back together. Unity games tend to mean that the actual upload size increases, possibly because of a large number of contiguous zeros.

There is no real trick in the stages between you upload your file and the installed size. You need to make sure that the build that comes out of Unity is as small as possible through careful use of texture compression etc.

So, in summary. A 60Mb IPA which you submit to apple, might be a 90Mb download which then turns into a 300Mb application when installed.