Maybe I'm being a bit thick, but the way I'm thinking of it is this:
Flying near the pad, it doesn't really mean anything much to me what power I need to fly S&L at BROC speed, but what I'd really like to know is what power I will hover IGE (or OGE for that matter, preferably both) with.
Then I can either use a predicted or allowable maximum power, or even better, pull to one of the limits and see what's available, and apply whatever margins I want to allow for approach/departures.
eg. hypothetical helicopter - say it's TOT limited in the conditions I want to land at, arrive in the area, pull to the limit and check how much Tq available. Fly at my magic speed that equates to IGE (or OGE if I have a speed for that) hover power, then I can say - OK, can pull 97% Tq at the TOT limit, I will need 88% to hover IGE, got a 9% margin which I know is heaps for an angled approach to the IGE hover. Or something along those lines.
Flying at BROC speed doesn't really help with what's going to happen in the hover - or does it??