Yay! Another hair twin!
It's hard to tell from your avatar but it does look like my hair!
My hair also pulls red, turns redder in the sun, etc. But I like it that way, just not too much of it. So I use a neutral shade and get warm highlights where the gray is.
The mix of ash brown and ash brown might still work for you, you'll just have to experiment how much of each to use. Maybe 1/2 and 1/2 or less brown, more blonde. And your timing will make a lot of difference. I leave my color on for 50-60 min to really soak into the resistant gray. If you don't have that problem, you'll have it on less time and it won't get as dark then.