I have an Orion XS that goes to bulk for about ten seconds and then directly to float when the van starts. Battery bank voltage doesn't seem to matter. Although, I've only been down to 80%. MPPT 100/30 it's doing great, but not keeping up on long days with A/C running.
Setup: 2 x 280 ah Dakota Lithium in parallel. Multiplus ii 12/3000/50, Smart Shunt, MPPT 100/30. Absorption set to 14.4v and float set at 13.5 v.