The only reason to float the battery is to buffer the charge/discharge requirements.
The float voltage chosen will depend on how fast the recharge should occur and what SOC needs to be maintained. There was a study of calendar ageing vs SOC (Journal of The Electrochemical Society, 163 (9) A1872-A1880 (2016)) which showed a 6% loss of capacity over 9 months for SOC between 80 and 100%, 3% loss for SOC from 40 to 70% , and no loss at 0% SOC . If the 40 to 70% range was used, there would be no worry of overcharging and not much worry over recovery rate.
In this case a float voltage of 3.315V might work well but I would have no confidence that I was working up against the 70% SOC desirable for energy storage. In my case, I want to keep as much energy on hand as I can and since there is no difference in ageing from 80 to 100% SOC, I want to push the 100% and overcharging becomes a worry. I use the variable source solar PV and the load is various things in my house. I looked at some fractional C charging rates which I posted here. For floating, the green curve in fig. 2 is most useful (You will see that a higher voltage is required for charging, then you can drop back to float). For my purposes a float of 3.40V seems to be a good compromise between responsiveness and risk of overcharge. One of the A123 cells specifies a float of 3.45V which is higher than needed for my QH cells (https://www.lifepo4-batteries.com).