Crab's post is the most valuable of all here. For confined area landings you must indeed be able to hover OGE as an absolute minimum, and the 10% margin is important.
Calculations of AUM for OGE hover are important, but even more critical is practical proof you can indeed hover OGE, with your acft, there and then. If there is any uncertainty, I like to try and bring the machine to an OGE hover, nearby the landing site, and see what power I'm using and what the reserve is. And high enough (eg 200ft) to regain TL afterwards if it can't be done. And when doing this it's vital to be patient and let the acft stabilise in a genuine OGE hover, for as the last 20kts bleed off, the power rise is big. Ok I know it might be in the avoid curve, but the risks of engine failure then are miniscule compared with risk of running out of lift and crashing on the way in.
If you pass the HOGE test you can approach the CA into wind with confidence. If not, you know you were right to divert to a clear area nearby and call for a lift.