Hello Sander,
1. Polarity Setting: Positive polarity means more white results in more positive sensor voltage. Neg. polarity is a lower voltage with more white pixel. Most CCD sensors are negative polarity. Many CMOS and CIS are positive (with exceptions). Polarity select gives you that flexibility so that AFE digital output will always give higher digital value for more white, if polarity bit is set properly.
2. Input Voltage Range: The voltage range I've been quoting is for the benefit / linearity of the front end. There is additional analog offset and analog gain (having a very wide range and reach) which are incorporated inside the LM98620, as shown on page 3 Block Diagram. Even if your input swing covers only half of the front end linear range, this does not mean your digitized output is missing 1/2 the dynamic range / bit count. If you have a choice, it is always best to go with as big an input as possible, and then use less gain within the AFE for higher performance.
For your particular large input condition, you can break the external / board connection between VCLPINT and VCLPEXT (and still use a large cap on it), as shown in Figure 15. Assuming a negative going signal, you would then use VCLPEXT voltage close to the top end of the input voltage range 2.25V as the best setting for your input.
Regards,
Hooman