Its calculated result correct?? See the linked picture from my friend laptop specifications. -->
https://i.kek.sh/zUjUwL6MVZE.jpg
Example: Intel Core I3-1005G1 CPU, Win10 x64 with 8GB memory. (Total cores: 2, Total Threads: 4)
Available physical RAM 8GB --> 8589934592 byte
PreCalculate: 0.65*8589934592 = 5583457484,8
Cores --> 4+1 = 5
Final calculate: 5583457484,8/5/1048576 = 1064.96 MB?? Try it added extra /8 values? 132MB values its really.
Use -mtt1 and -mt4 mode and -d128m dictionary size, eats 5.2-5.5GB's memory from during compression.