Hello Capt Tosspot,
I would rather use the chart 14 "maximum take-off and landing weights on helipads" in supp 1(cat A ops) of the RFM.
It shows a MTOW of 3320 Kg. Your DL is then: 3320-2800= 520 (to share between payload and fuel)
The take-off profile is the vertical backward climb to CDP (130' height) and you need a minimum helipad surface of 21 m, this garantees the 35' clearance in case of engine failure at CDP.
If your helipad surface is >= 105 m (or "confined area) you can vertically climb to CDP (instead of a backward climb)
You'll also have to work-out you obstacles clearance on your take-off path (charts 15 & 16 "climbing performances")