It might be easier to tap off the battery, and draw power as it approaches the voltage cutoff for bulk - IE have some load that pulls just enough power to maintain a battery voltage of 14.2-14.3 Assuming it bulks at 14.4. The batteries would absorb as much as they can at 14.2-14.3 and the diversion load would get the excess off the panels. When the batteries are truly low, they would get full solar power until they hit the 14.2.
The idea is the solar maintains full output, the batteries taper down, and the diversion load increases to maintain battery voltage.
Might as well loose the charge controller, and only have voltage limiting on the battery by the diversion load.
