Dalvik vm heap props resetting on reboot

I am running android 9 and I tried changing heapsize prop by the following command setprop dalvik.vm.heapsize 384m and then verifying by getprop | grep heapsize which returns 384m so it works. But after a reboot the value returns to its default 768m.I also tried to modify the build.prop file by adding the lines but still the props revert on every boot (the file itself still shows the change). Any help ?