They tend to put such vital info as kernel parameters and "cheatcodes":
on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying 'Beware of the Leopard'."
Additionally they tend - at each distro release - to change some of them.
So, yes, it is not easy to find them though obviously some "general rules" do exist.
That is the idea behind the already given thread:
and of of this (hopefully successful) just born initiative:
More generally, any Linux distro uses more or less one of the three loaders:
- GRUB (legacy) <- (syntax compatible with grub4dos)
Additionally on their specific distro's Forums there may be "hints" or "full entries" for particular configurations.
So the "job" is to examine the specific entries in one of the three configuration files, and "translate" them to the "other" loader you choose (if possible).
Then test if the translated stuff actually works.
Since the good Linux guys mostly ignore grub4dos - which is probably seen as a somehow "unauthorised fork", MS friendly, of the "real pure linux" approach and IMHO the most flexible of the lot - they traditionally also ignore full .iso booting, often putting inside their releases *something* in initrd or however inside the .iso that is hardcoded or incompatible with .iso mapping.
Hopefully now that GRUB2 allows for using .iso as loopback, these incompatibilities may decrease and most distro's will become compatible with .iso booting either with mapping (grub4dos) or memory mapping (both grub4dos and Syslinux/Memdisk) or .iso loopback (GRUB2 and BURG), but as said, instead of focusing on "which is the best loader" (as you seem like being right now) you will have more and better result by flexibly choosing the actual loader for which you can find a working syntax and use whatever is easier to get the stooopid .iso to boot with.