This is similar ish to what we often do.
We typically do 5% to View Content, 5% to ATC at the top (so 10% total), exclusions handle the new reach for us, and it’s validated through lift studies. Interest targeting works for us at BOF, sometimes up to 25% of our spend.
Every account is different tho
Take your top best performing ads.
Launch a sales campaign, but instead of optimizing for purchases, optimize for daily unique reach.
Launch that campaign at like 5% of total spend.
To me this has been the biggest contributor overall to pushing net new reach on Meta.
The key here is the audience and placements seeing the content. Advantage needs to be off. Customize the placements. Exclude all engagers and buyers.
I've found launching with interests actually seems to push things higher. Use your cohorts to understand the demo and just send that signal.
I usually am a broad maxi, but for these I want a bit more control. I've found if you do give the reigns to Meta it generally does the opposite of what I wanted.