in my eyes, a theoretically sound scale roughly by the number of voxels, which is the amount of information. a fudge solution would probably be a scale ~N, which i also did for the saxs restraint.
I agree that we aren't too a point where we can have a bulletproof solution. However, given that the problem comes up again and again, it seems reasonable to take people's experience so far and use it to develop guidelines for how restraints should behave and rules of thumb to provide better starting points for other users. In addition, the more awareness of an issue like things permeates things, the less likely it will be that someone is surprised. For example, if the docs for the EM restraint say something about "The EM restraint should be wrapped by the ScaledEMRestraint wrapper which scales the CC scaled by the number of particles and a factor for X so as to bring it into scale with the other restraints", then anyone who uses the EM restraint will know to think about scaling.however, as the solution of scaling different kinds of restraints is not really solved anyways, i do not quite see the point of putting a pre-fixed solution, as it pretends to have found a solution for something where it has actually not been found.
As it is, people will, as Keren did, occasionally simply add restraints to a Model without thinking about scaling. Or will change their representation scale, and wonder why nothing works any more.
I suspect that we can get 80% of the way there (with something like what I suggested), which should be good enough for many applications and to keep a bunch of users happy.