The Threshold slider works only with the division of the option activated.
To increase the use of RAM you can try modifying "arc.ini" in the "Resources" folder for the use of external algorithms (LZ77 & XZ)
Code:
[External compressor:lz77]
header = 0
packcmd = 7z a -txz -an -mcrc=0 -m1=lzma2:dXXXm:fb=273:mf=bt4:mc=1000000:lc=4:lp=0 -mmt=2 -mx9 -si -so <stdin> <stdout>
[External compressor:xz]
header = 0
packcmd = 7z a -txz -an -mcrc=0 -m1=lzma2:dXXXm:fb=273:mf=bt4:mc=1000000:lc=4:lp=0 -mmt=4 -mx9 -si -so <stdin> <stdout>
6GB = lz77: 300 / xz : 150
8GB = lz77: 450 / xz : 250
16GB = lz77: 1200 / xz : 600
With these modifications do not assure you the proper functioning..