Hello Martin
It seems you are becoming confused about how to apply the various bits of guidance on maximum weights and loads.
Lets deal with 85% figure. This relates to the maximum weight of the caravan expressed as a percentage of the tow vehicles kerb weight.
First of all this is not a rule it is a guideline offered by the UK caravan industry. It has no basis in law, and no country uses or recognises it. However, I do believe that in term of conventional caravans it does make a sensible target, especially for an inexperienced tower.
What you are allowed to tow is determined by your licence categories, and the maximum permitted tow weight as defined by the vehicle manufacture for each make and model of car.
The nose weight is a separate issue. There is a legal requirement which I believe is defined as a minimum of 4% of the MPTLM of the trailer or 25Kg which ever is greater. The upper limit is defined by the towbar rating of the car, or the hitch limit of the trailer which ever is lower. So you have a window of legally acceptable nose weights. The 85% figure has no bearing on this figure.
In general it is suggested that you achieve a nose weight which is towards the maximum that your combination will allow.
'Practical Caravan' has a straight forward guide to towing law at the following address
http://www.practicalcaravan.com/legal/index.html