can't enable tonemapping on mobile previewer o mobile devices???????

Hey

i downloaded UE 4.18 recently and created a project then switched to mobile previewer and typed in the console
“r.TonemapperFilm 1” and it worked fine and now when i create a new project and try to enable tone mapping on the mobile previewer its not working at all and tried to add it to DefaultEngine.ini following the documentation still not working the only command that work is “r.Mobile.TonemapperFilm 1” but it only work for the session please help.
one more question can i choose what devices to work with tonemapping and what don’t like enable tone mapping on high end and disable it on the low end???.
forgive my bad english.

I haven’t even been able to find the mobilepostprocess/config file…