Current:
iPhone 6 Plus and iPad Air 2 here + iOS 9.3.2 + clean install version
You go in other room, in this case 10m + 2 walls + 2 doors.
Then activate iOS wifi personal hotspot in this room. Bluetooth is off. Only mobile data and wifi personal hotspot is on.
In other room searching this wifi hotspot not working. Signal not available!!
With my old iOS devices same issue iPhone 3gs,4,4s,5. Reset? Not fixed!!
Hardware issue? No. The iOS devices in Apple-Store same issue. I said this issue in year 2011. And now? year 2016 with iOS 9.3.2. not fixed!!
Android devices wifi personal hotspot Samsung Galaxy S3 (Android 4.0),S5(Android 5),S6(Android 6), Huawei Mate 7(Android 5), Sony Xperia Z(Android 4), Google Nexus 5 (Android N preview), iMac 2011 (OS X 10.11.5 wifi ad-hoc). No issue.
If searching this wifi hotspots signal good-very good. Signal available!!
Not forget Samsung devices have Broadcom wifi-chip as the iPhone or iPad.
I wait since iOS 4.3 on the bug fixes.
Second issue:
iOS wifi personal hotspot not support, create wifi hotspot without mobile data. This is very good for webdav server.
Android or OS X/Windows ad hoc no issue.
Third issue:
iOS create wifi personal hotspot not possible
no support for prepaid card (MVNO) with this APN.
Android, OS X/Windows ad-hoc. No issue.