As T1 suggested, the Tracer units did not play well together when connected in a simple manner. One (or the other) would remain on float whilst battery load tests dropped the voltage into "bulk" zone. Not always, just sometimes. Hmmmm.
HOWEVER, with a little re-wiring -merely doing it properly in the first place

The battery consists of a bank of 4, supply is taken from terminals on inner two batteries. Charge from the Tracer units is put into the outer batteries, as far from the outgoing battery supply and the other tracer input as possible. This seems to filter/buffer the read voltage to a smooth enough figure which both MPPT regulators can operate together nicely.
This setup should do me until more panels get added or a Li upgrade. Once again, thanks Terry for your advice
