Stamping and Embossing

If there is a hairdresser or someone that knows hair out there I'd really appreciate a little consultation.
I am a dark brunette Level 3 and I am trying to refresh my hair color one or two levels since anything more would turn me brassy, I have a lot of red pigment.
I did a strand test using 5A-Light Ask Brown with 20 Developer and I even added Ardel additive to avoid brassiness.
The hair where I did the strand test turned brassy regardless. Do you know if I use 4A with 20, if I have a chance to avoid brassiness? What about 3A with 20?
I was told by the Ion hotline that if I use 3A with 10 it'll just refresh my naturally dark brown color. I don't know what would happen if I use 4A or 5A with 10.
Any advice would be helpful. Thanks!