In looking at my previous post I see that, when answering Xnr's point about obstacle clearance, I have committed Nick’s heinous sin of quoting regulations.
What I might have said was if an Authority wishes to ensure engine failure accountability (particularly in a built up area) it must specify the minimum obstacle clearance standard - not to do so would be to ensure that the twin is less safe than a single as it has double the probability of an engine failure with the same consequence.
FLI - then you have to turn to the AB139 within its present MCTOM (MGW) or fly one of the FAR 27 twins. I personally would accept PC1 where it includes a variable FDP with or without a modified RTOD. As has been said in previous posts, without OEI HOGE, a set of flexible procedures that give a continuum from the helipad through the confined area (short field) to the clear area would be a goal for the manufacturers to aim at.