cassandra heap size config

Currently, the cassandra_stress_benchmark does not run on some instances types due to not enough heap in JVM, for example C4.2xlarge.
The default max_heap_size used is max(min(1/2 of the memory in the vm, 1GB), min(1/4 of the memory in the vm, 8GB)). In a C4.2xlarge vm, the max_heap_size is only 3,4 G.
Should we just leave the configuration as it is (mostly default), or try to tune the configurations a bit (increase the ratio of max_heap/memory on vm) to allow the benchmark run on all instance types and also allow users to change configurations?