I think everyone who remain profitable scale the same way:
You do increase budget slightly (10-15% usually at once) and check whats happening with the ROI for 1-2 days.
If your ROI is acceptable you increase 10-15% more and wait few days, and do this until you get break even and then stop and decrease budget.
Me personally never increased budget too much even if I kew I would still be ROI positive, because I like to make little less but longer, and in long term I win more with this technique, otherwise I would pay google/meta too much money for ads, and a part of them could be my profit.
P.S. this also depends on your budget, you do not increase by 20-50% a budget of $1000-$5000/day, because you could loose all your previous profit instantly. But a budget of $20-$50/day you can increase by 20-50%
Update: about your question "When should I scale?...
You scale when you are ROI positive for few days at least, or you scale when you are ROI positive same day but on bigger budgets.
Also you must look in the history and check WHEN exactly you are getting best ROI: I mean which part of the day and which day/s... You could increase budget for that time only.