Using 2 separate solar panels with the included 4 prong to XT-60 connector

Hi, yesterday I tried using 2 separate 200 watt solar panels with the included 4 prong (2 negative, 2 positive) MC4 connectors to XT-60 connector to the Elite 200 v2 and I tried hooking it up and it just wasn’t working for me. I hooked up both panels to the 4 prong connector cord which led to the bluetti elite 200 v2 power station and with both it would be at 158 watts and about 19.4 volts. Yet, with only 1 solar panel hooked up it went to 146 watts and about 17.4 volts.

Then finally, I asked A.i. and it said to connect them in series, which means to connect the positive cable of one solar panel to the negative of the 2nd panel and then hook up the remaining connecting leads of the solar panels to the mc4 connectors on the included cable that bluetti included in their packaging. It worked!

That tells me that if i wanted do, because there is still an available spot to connect 1 or 2 more solar panels if i so desired. I could have gotten out my 400 watt solar panel and then hooked that one up to the remaining connectors if i so desired and that would have added even more wattage to charge the power station?

or even 2 more 2 separate 200 watt solar panels???