Neither of the team's drivers have scored points since September's Singapore Grand Prix. It has lost all hope of beating Lotus to fourth in the constructors' championship and is at risk of losing fifth to Sauber.
The team introduced a major upgrade package, headlined by a Coanda effect exhaust, in Singapore.
Haug said the need to fully master these developments, plus efforts to upgrade Mercedes' windtunnel programme, meant the behind-the-scenes progress was not yet being reflected on-track.
"We certainly do not get the full benefit of this Coanda technique currently," he said when asked about Mercedes' issues by AUTOSPORT.
"You cannot get that after two or three races. You have quite a high price to pay in terms of fuel load and horsepower and so on, and I think you have to compensate, and I think that is not quite happening.
"But there is no other way to find a solution than to explore it.
"We have had, and this is not an excuse, a period of one-and-a-half to two months where we changed from 50 to 60 per cent [windtunnel] models.
"You need to do that to prepare for the future."
Haug insisted that now Mercedes had proved it was capable of winning grands prix, there was no reason to doubt that it would be back at the front of the field once its current problems were resolved.
"We did not get a win as a present," he said.
"The [Shanghai] track suited the car, but it was still one of the most dominant wins - it was by 20 seconds and it could have been a one-two," he said.
"We were certainly fast in Monaco, we were certainly fast in Montreal. There have been probably a handful of races where we looked pretty competitive.
"But it's right to say that since the summer break we are not where we want to be, and there are reasons for that.
"One is that we need to explore the Coanda exhaust. This is certainly not giving us the full benefit currently in my judgement. On the other hand, we need to do this windtunnel programme for sure.
"If people criticise us, then we fully accept it, but we have been there [at the front] half a year ago, winning a race not by luck, and we're working very hard to get there again in half a year's time.
"This is our programme and this is what we want to achieve."