IME when in float, the power needed comes from the battery for a few seconds until the MPPT controller provides as much power as the panel will allow, which should be 100% From the panels if the energy is there.
I had Trojan FLA batteries and charged them per specs, and it worked fine.
I switched to lithium batteries, and I had to tweak my Bulk and float settings to get this to work, but I it did. These settings were slightly different on the two different systems I have with lithium batteries. The lithium batteries were built from cells which only had a charge no higher than rate, not bulk or float.
IF these are lithium batteries, AND there is no spec sheet for them, you MAY consider increasing the float voltage. At first on my lithium batteries in float, the MPPT only used 30% of power back into that I was using. A 300 watt load as pushing 100 watts back in with 900 watts of panels. I stepped up the float voltage in .1 VDC increments until I was at 300 watts from the panels.
By doing this, there is some risk that the lithium batteries won’t last as long because they’re floated too high. If I did not do this, I risked going into the night at a 30% SOC because charging was done early in the day. Regardless, I WOULD NOT go against what a spec sheet says.
IME, in full sun my portable panels pointed at and angled to a noon time sun will provide 100% of rated power in March; however, my rooftop flat panels will provide about 60% of rated power.