RE NetCommunity plugin does not allow an online payment to be linked to both registration fees and additional donations - it has to be one or the other.  There's no warning for this, and the official solution is to manually create a new gift in batch for the additional donation.  Everywhere in RE, registration fees and additional donations are treated as separate.  In BBNC event registration parts with additional donation enabled, the additional donation field looks like an afterthought.  All we, the users, want/need is to have a "donation" or "contribution" price level, and have the option of not using a fixed amount online.  Then, the donation is just part of the registration fees, it doesn't slow down NC plugin processing, it shows up in reports without having to break it out, and it looks much better as part of the event registration process.