I've made 3 angel investments in the last 6 months and can honestly say, no ROI calculation figured into my decision-making.
In each case, a combination of the team and product was what made me want to invest.
I'm also lucky enough to be backed by great angel investors in my own company. I can tell you that ROI would be a low-ranked decision for them too.
Valuation does matter. But ROI really isn't a driver.
The hope is that the investments return enough to do more.
That IMO is the thought-pattern of true angels not to be confused with investors who want to invest in early-stage companies motivated mostly by the hope for amazing returns. If making money is the primary motivation, I wouldn't want them investing in my company. It means they have zero value to offer whereas the angel round is where the most value is most often needed by the founder(s)
Happy to talk to you in a quick call to explain more of the mindset and if you're considering investing or raising, share some more advice.