Hi Gulfstreamaviator
The 50ft addition to the MDA on an NPA is only applicable if you wish to conduct the NPA using Constant Descent Angle (CDA) techniques. I don't think that the JAA (which doesn't exist anymore BTW) insisted on this. If you wish to employ 'dive and drive' techniques, there is no need to add anything. I think it is true however, that the provisions of EU-OPS and the UK CAA strongly recommend using CDA techniques when conducting NPAs (as do the Flight Safety Foundation).
The MDA remains as published, but the CDA technique requires a Decision Altitude (DA), rather than an MDA.
In other words, when you reach the DA, you either initiate a go-around or continue to land, depending on whether or not you have adequate visual reference. With the CDA technique, you do not level off at the MDA and fly towards the MAPt before initiating a GA. This is similar to the DA employed on an ILS approach.
The reason for the 50ft addition now becomes clear: it is there to enable you to make a decision to GA without descending below the MDA during the manoeuvre.
By contrast, if using the 'dive and drive' technique, you plan to level off at the MDA, so no addition is required.
For a 'circle-to-land', again you are planning to level off at the circling minimum, so you don't need to add anything.
Unfortunately, I don't have the EU-OPS reference to hand. I am basing my response on the practises employed by UK PT operators. I don't think this info would be in LASORS either.
When using this CDA technique, it is important to remember that the GA must be continued straight ahead until passing the MAPt, before any turns may be commenced.
Hope this helps,
Eck