Solved: Limited IQ8+ inverter output
So whatever the Vmp under these conditions, times what ever the max amps from the panels the IQ8 will accept seems to be 250 watt. Even if the panel was able to provide more amps, the max voltage of the panel (only 54 cells) and the max amps of the input of the IQ8+ sets the max limit of power converted hence the flat line.