Well I did some tests...
Game: Age of Empires II HD The African Kingdoms
Size: 4.45GB
Reflate+SREP+DELTA+LMZA size: 1.66GB (My bad here, i forgot to leave reflate+lmza only)

everything looks promising till there... when i test the installation, starts installing without problems and suddenly it gets stuck and it's been like 8 hours since it started the program is still running (no crashes) but still doesn't finish the installation...

I as well did some further tests & it creates an error, used reflate+lzma
Tested twice more on other conversions & same unpacking error.

Replace reflate in UA with reflate_std.exe from here
http://nishi.dreamhosters.com/u/rawfilt_v1l1.rar
also rename it to reflate

Note : This one is Compiled with GCC so amd users can use it.

Also Razor if u have some time can u make dll for inno which can show progress with this
http://nishi.dreamhosters.com/u/7zdll_vE5.rar
this one has inbuilt shelwein's rep, reflate, zstd ,zstd_mt and much more and also split** function for multi-tasking and also it is regularly updating
i can use ISDONE's ISEXEC2, but it not looks promising and also ISDONE's Unpack 7 zip feature only support 7z format and this one has its own format "PaFiLe"
Thanks in advance

^^ What good would that do to use reflate NOT in the package update Razor' supplied, everyone would have to add it as well to be able to prevent the errors above mentioned.

UA 2.5 still has errors, compresses fine, but refuses to extract. 1 of 2 errors:

1- Setup.exe has encountered an error & stops installation.
2- Starts extraction process but stalls at X%, & sits there forever.

Ive checked 3x that the files from the update are in the correct folders, but the mentioned issues are still the result.

Wouldn't the ISS script need to be updated as well ?? as that seems to be an issue with the resulting Setup.exe
cannot extract the files if MSC,lzma is chosen compression method, works fine otherwise ( anything else without msc )

Same here. I don't know much about such things, but Setup.exe really knows how to unpack "reflated" archives, when no function for reflate is in InstallerScript.iss? I can't believe that only add two files in "Include" folder and script make wonders :D

Testing right now, edited ISS script and replaced MSC.exe with Reflate.exe
added the 2 other missing files cls-msc.dll & cls-msc.ini, in all needed locations BUT still error. Always fails CRC check error message, so something
else I'm missing within ISS script.

which version of what script are you using ?

//PrecompVer=inside To PrecompVer=inside

Have you tested reflate by enabling PrecompVer?

reflate No Test
pZLib Yes:D

Hi. Sorry for this question, what is the reflate version executable or where to find of this cls and parameters in arc.ini ?. Thanks

[External compressor:reflate]
header = 0
unpackcmd = reflate -r2 -t75p -p5 -ht1 -ht2 -b2m - -o - <stdin> <stdout>

does NOT work in the current version of Ultraarc, Setup.exe issues when trying to extract files when using reflate option.
NOT in arc.ini, but within ultrarc.ini file itself. File that has reflate update in the name is the file your looking for.

Alright thanks. Where find the updated reflate executable ?.I only has the cls dll file and i need the executable for testing.

within the latest UltraARC Resources subfolder.