gearbox and chain drive efficiency
We were using a Brevini box and #180 chain, but Bonfiglioli were giving us similar numbers, they just couldn't deliver in time. We ran into efficiency issues with the air system ( CV losses through valving and plumbing) that impacted us as well as simple mechanical losses in the bearings and such. I'd suspect your losses are hydraulic and mechanical. I never did find any data that conflicted with the assumed chain efficiency. everything we found was the same value, almost as if they all came from the same paper/study (which is entirely possible.) I did not make an effort to isolate chain efficiency vs mechanical losses. Sorry.