OK, I maybe didn't ask that as well as I could......
Does the entire rear cross beam that your rear rollers are fixed to swivel on an axis parallel to the trailer axle, the roller sets rigid fore / aft to the beam, but each individual roller axle pivot independantly? Or is youre beam fixed, and the two banks of rollers tilt fore & aft independently?
Now to try a better explanation of what I was trying to say. Yopu'll need your 3d imagination hat on here......
If that entire rear beam swivels , rigid with the two sets of rear roller assemblies, what happens is the "v" of the beam is pushed forwards out the way as the two rearmost rollers meet the hull. (they are pushed down, whioch swivels the entire beam so the bottom of the "V" moves forward out the way) With a centre (keel) roller, the keel will hit first, and the boat will then want to "capsize" until the side rollers touch the hull. This is especially so if you have a rigid straight rear cross beam, as the keel roller will not move "out the way", and gravity means that it will want to go sideways for longer (until the side trollers touch). this phenomenon is ineviable with any "pointy bow" boat. Hence, the "hiding to nothing" because it's inevitable the boat will overbalance on the keel roller before it is supported by the side rollers.
If you look closely at the Oceantrail pic, or the one on here shows it better: http://www.indespension.co.uk/b2c/ap...ID=1090&slnk=1
you'll see the rear rollers are welded solid relative to the beam (can adjust left / right to suit the hull) and the entire beam is hung from a couple of large bolts at the chassis - the whole lot pivots as one.
If the whole beam swings and there is no centre roller, as you winch on, the rearmost rollers touch the bow first, and the weight on them swings the whole beam so that the rear roller banks are at a silly upwards angle. (as per the indespension pic) As you winch further on, the bow starts to widen out to form the main hull, gravity takes over, and gravity takes the boat to the lowest point (which prety much parks the keel dead centre betwween the rollers. Once the rollers are past the "pointy" bit of the bow, the beam aligns itself relative to the keel, and as you winch further on, the hull rolls up this self aligning slope until it starts to overbalance (the centre of gravity of the boat passes the pivot) and the whole beam and boat then swivels in unison to "horizontal" and the bow is caught by the forward rollers. (forward rollers don't need the whole beam to pivot because the boat is by definition already lined up when they touch the hull). Once that has happened, you have a full set of rollers aligned & you just keep winching 'til lit stops.
You say your rollers are further apart. On a full swinging beam, the spacing will depend mostly on the shape of your bow, as a "bulbous" bow will get to "hull" size quickly, so they can be further apart whereas a narrow bow will need the rollers closer together to prevent the keel form hitting the beam. Mine are probably on a spacing where the inner rollers are not too far off your keel roller width, and I have the forward ones set as far out as possible to stabilise it.
Looking at your trailer, your rearmost cross beam (the one that holsds the rollers) looks straight from those photos. I can't easily tell form the photos, but I think your fore & aft roller beams on the rear beam pivot relative to the beam rather than them being rigid to the beam & the whole beam swinging? Thing is that there is a relatively small angle the roller sets can swing through if tyhey pivot relative to the beam, so you inevitably end up with just the rear two doing anything at the beginning. Couple that with the narrowest point of the hull (the bow) which means that the rollers are "too far apart" to hold the bow off the metalwork, the bow will inevitably hit the beam, I assume that's why the keel roller is there, and as discussed already that instantly gives you an instable system.
Lots of words, hope they make more sense than last time.