Low solar input

I have the Delta to max and one additional battery and have it connected to three renogy solar panels hundred watts each. The three panels are connected in parallel with a combiner box and using an XT 60 I cable. I’m having trouble getting more than 75 W of input under ideal sunlight conditions.

I have been advised that the XD 60 I cable I’m using may not be configured properly and I should get the cable from EcoFlow. I have also watched videos of people modifying the cable by connecting the negative side to the middle pin by soldering it.

Any suggestions on how to increase the wattage input from the solar panels would be appreciated.