Just as a point of reference, using 5.080V will still provide more charging with a 6V Solar Panel in Cloudy Conditions. See the general graph in this post
I agree, it's my opinion that SourceMaxCurrent isn't near as useful at SourceMinVoltage for most circumstances involving Solar Panels. Solar Panels are 'Current Producing" sources, but we cant do much with current if the Voltage isn't higher (+ a minimum Overhead) than the battery that we are trying to recharge. That's where the PMIC's DPM (Dynamic Power Management) shines on two fronts.
By using powerSourceMinVoltage(5080), the PMIC will operate the 6V Solar Panel at the max effeciency that it's able to, no matter the light intensity.
Here's a clip from the datasheet:
8.3.2.2 Dynamic Power Management
To meet maximum current limit in USB spec and avoid over loading the adapter, the bq24195L, bq24195 features Dynamic Power Management (DPM), which continuously monitors the input current and input voltage. When input source is over-loaded, either the current exceeds the input current limit or the voltage falls below the input voltage limit. The device then reduces the charge current until the input current falls below the input current limit and the input voltage rises above the input voltage limit.
Regarding the Li-Po termination voltage, it's just personal preference based on each project's goals.
If your Li-Po can meet your Design Power Budget with it's remaining capacity at 3.9V, then there's no harm there.
I feel like the default of 4.1V is a great "all around" number.
I've even started switching to 4.2V during the Winter Months for most Li-Po Solar Projects, as it helps tremendously during a cloudy week or two.
If space isn't an issue, then a 12V Panel and 12V SLA make life easy, as Power & Sleeping are no longer main aspects for the Project.