The Neoload controller - NeoloadGUI and NeoloadCmd use the following files respectively (you will only use one of these at a time)…

C:\Program Files\NeoLoad 6.4\bin\NeoLoadGUI.vmoptions
C:\Program Files\NeoLoad 6.4\bin\NeoLoadCmd.vmoptions

In each file you will see the entry -XX:MaxRAMFraction=4, this means that NeoLoad will allocate a quarter of the available RAM to its JVM, you can override this fraction with a specific value such as -Xmx=12g, meaning that for a machine with 16GB, we will use 12GB for Neoload GUI plus the 2 agents (1GB) so 13GB used by the controller and 3GB for the OS

For the LG, there are 3 files, two for the LG agent (LoadGenerator.exe or the windows service) and one for the LG engine (the actual LG launched by the LG exe/service).

Agent: C:\Program Files\NeoLoad 6.4\bin\LoadGeneratorAgent.vmoptions (or LoadGeneratorAgentService.vmoptions)
Engine: C:\Program Files\NeoLoad 6.4\conf\agent.properties

The LG agents vmoptions file has the following value -Xmx512m, this can remain small as this agent is effectively a listener waiting to hear from the controller. The agent.properties file contains the JVM settings used to launch the LG engine itself (this is the important one). You will see this entry lg.launcher.vm.parameters=-server -XX:MaxRAMFraction=4 -Xss228k, again you can replace the fraction value with a specific value such as -Xmx=12g, meaning that for a LG machine with 16GB, we will use 12GB. In this example my LG would be using 12GB + 512m.

I’m not sure I follow your logic and have never seen the -server switch before but on the controller, these settings change the embedded LG on the controller aka localhost:7100