Hi TRR,
I looked at the track plan and see the curved approach to the 90° cross. The SD-70 has two collectors that appear to provide sufficient spacing to compensate for the hot or the wheels being insulated momentarily.
I have not had one in my hands, so I don't know what MTH does underneath electrically in their cross. Would you post a photo of the bottom? You may have to solder some jumpers to provide connectivity through the cross.
The other setup I don't like about MTH RealTrax is that only one outside is connected to common. I have been soldering a jumper to the common contacts on a layout that I am restoring, so that both outside rails are connected to common.
perhaps, if you put a lock-on on a track on the loop inside of the cross with the opposite outside rail to the first lock-on. Then run wires from the first to the second, color matched , of course. The 90 may be isolating that inner loop.
