upgraded from ts8320 to TS9020 (serious question)

[mahdi89]

i have upgraded to ts9020 wich claim to have 9600*2400 dpi resolution

while ts8320 is 4800 x 1200 dpi

 but i have found that they both have the exact same Printhead "QY6-0090"

how can one achives higher resolution while using the same printhead?