Having been using DOS80 for a while now, the extra capacity is very useful but the big disadvantage is that the four different available formats (200k, 400k single sided, 400k double sided, and 800k) are not compatible with each other. For instance, once my Drive 1 has been configured to work with a Gotek 800k image, a reboot with a different DOS disc is required to read a standard 200k DSK image on the Gotek. That's a bit of a pain!
An even bigger pain is that it not possible to copy files from one format to another on the same drive. For example, if the Gotek is set to 800k, copying a file from a 200k Gotek image on the same drive would require rebooting the Gotek with a 200k boot disc, then copying the file to a second drive before rebooting to 800k again. Quite an inconvenience, particularly if your boot drive is the original 3 inch drive!
So I tweaked my DOS80 boot disc to change between different capacity images on the Gotek without needing to reboot DOS 
This is so much more user friendly and useful!
All four formats have the same 2k block size and have 10k reserved for system track/s. The only real difference causing the incompatibility is the space reserved for the directory entries. All the larger sizes (400k and 800k) have 4k reserved for 128 directory entries. The standard 200k format is different in that it has 2k reserved for 64 directory entries.
So I modified a DOS80 boot disc so that the larger formats have the same allocated directory space as the standard 200k format. This ensures compatibility and enables file copying across different capacity formats on the same drive!
The downside is that it's possible to run out of directory space before the disc is full, but the worst that can happen is that DOS reports a directory error. How quickly this happens depends on the number and size of the files saved. The maximum capacity is 64 files of 16k or less which is generally more than enough files on one disc! Even with an larger size of 32k there's directory space for around 32 files. So the restriction of a smaller directory is actually not too problematic in practice.
In order to benefit from a larger disc size and reduce any potential directory capacity issues, I've chosen to use the DOS80 Option C 400k format (390k Total) for my Gotek in Drive 1, modded so as to be compatible with both 200k and 400k formats. Two bytes need changing to modify a DOS80 boot disc so the single-sided 80 track 400k format (Option C) has 64 directory entries rather than 128. Fixing the drive at 400k means that DOS displays all images in the Gotek as having '390k Total'. This affects 200k images in that the displayed number of total free bytes appears wrong, but this inconsistency doesn't affect the accessibility of the files. So I know when I see 390k this means the modified DOS is operational with capacity 'up to 390k' (if the working image in the Gotek is big enough). Obviously, if you try to write more files to a full 200k disc image it'll fail and complain!
With the boot disc in drive 0, the modification is done from MOS:
Type R 100 1B00 [ENTER] (this loads DOS into memory)
Type M 18E5 [ENTER]
Type 3F (to overwrite 7F) [ENTER]
Press [ENTER] (to leave 18E6 as 00)
Type 80 (to overwrite C0) [ENTER]
Type . [ENTER] (a full stop exits the editor)
Type W 100 1B00 [ENTER] (this saves the modified DOS back to disc)
Run CONFIG to select your Gotek as single sided 80 track (option C) and that's it!
You don't even need to bother about generating a separate custom 400k HFE or DSK image to use this format. You can use an 800k double sided HFE or DSK for this format too. But my advice is to format this with BACK80 so you can check it verifies as it should. As far as FlashFloppy is concerned the size of the disc image in the Gotek is determined by the stored values in the HFE or DSK, and the Einstein DOS relies on its own parameters. So DOS is quite happy to access only one side of the disc and ignore the other side.
I've left the 800k format (Option D) unaltered with 128 directory entries and this is still selectable by running CONFIG to change the boot format. And yes, I've an alternative boot disc that has tweaked this option to a whopping 1600k!
