There is no conversion to APFS happening at all. You format a volume as APFS using Disk Utility, and install High Sierra on that normally. Then, what the post-install patch does is simply shrinks the APFS container by 200MB, and creates an HFS+ partition in the freed space to use as the helper volume.
I can attest (redundantly) to your statement, given recovery process I implemented, after applying APFS patches and being unable to boot from main drive.
Long story short, I could not boot into my Main Drive, after applying the APFS patch. The patcher used was version 2.1.1
I did choose Main Drive as the volume to be patched for APFS functionality (not the recovery partition). When machine booted, while holding "option" button, I could see an EFI partition, Recovery Partition, main drive, and the thumb drive. The USB thumb drive held the patched beta 7 installer. All the post install patches were implemented.
Booting from EFI partition led to the "do not enter circle" (circle with line through center) followed by auto-relaunch of the installer on thumb drive. Booting into (fully operational) Recovery Partition gave me access to standard command set for that partition, but no way to "induce" boot into main (APFS) drive. Booting into patched Main Drive resulted with "do not enter sign."
I reformatted the USB thumb drive on another Mac, and installed new Beta 7, patched, installer.
Booted into thumb drive on laptop, reinstalled the new beta 7, and reapplied post_install patches patches.
Same "no boot" results.
Given the admonition that, one can't have both, an active Recovery Partition and a patched APFS Main Drive, I tried to find a way to eliminate the Recovery partition.
First try was via disk utility, which was accessible on the Thumb Drive. Oddly, the listing of partitions/volumes accessible through *disk utility*, included "HighSierra_BOOT" partition. That partition was not visible as choice when booted with "option" key pressed (the EFI partition showed instead). The bottom line was, I had to erase the ghost High_Sierra_boot partition, and recovery partition, and do so without destructive effect on my Main Drive.
A combination of terminal commands (while booted to Beta 7 patched installer) and the Disk Utility functions, allowed me to achieve that end (e.g., for terminal commands: "diskutil list" , "diskutil erase volume JHFS+ [and partition location])
I erased content of the HighSierra_Boot partition by accessing it via terminal, and then formatting that partition only, via sudo command. I then used Disk Utility to merge (empty) High Sierra_Boot partition with main container. It seemed the only way to proceed. Last step was reset NVram. The latter action, resulted in my USB thumb drive not booting.
Using a different Mac, I formatted the USB thumb drive yet again, "placed" on it the patched Beta 7 installer, plugged Thumb Drive into USB port of MacBookPro and used it to *successfully boot the laptop into the installer.*
I reapplied the necessary patches, and rebooted while holding the "option" key; this time High Sierra_BOOT partition showed up along with Main Drive. I chose the High Sierra_boot partition and it smoothly booted into Main Drive.
The installation run into one issue when I was asked to log into the iCloud - server error resulted. I skipped the iCloud step, and rest of boot sequence went perfectly. I checked the storage information, under the system report, and it listed as APFS.
Here are some oddities and some positive results.
==>When I logged into my account, on the fully booted laptop, and checked iCloud, iMessage and Face Time, all were
fully functional. That seems contrary to experience some others have had with those utilities, and odd, because I received an error message when trying to log into iCloud on boot (see above). Perhaps server connected later after all (?) Would geographical location have something to do with the problem, or Nvarm reset played a role in this process ?
Note also, that I never initiated a "clean install"; all the upgrades were installed over the "old system."
==> for some reason my graphics card is now listed as Nvidia 9400M 256 MB, rather than what is really in the machine, which is NVIDIA 9600M 512 MB. Could it be the effect of the auto-dimmer patch I chose in post-install process. The 5,2 MacBook Pro model technically should not need that patch (?)
==> system is stable and fast.
Hope this may be of help.