2016 Aygo speaker upgrade new ago new shape

[SHSHAH21]

Hi I use to have a 2008 Aygo and now i have a 2016 Toyota Aygo 2016. In the 2008 Aygo i had front door pocket Speakers and rear door pocket Speakers and i though the balance was okay and sounded okay. In my 2016 Toyota Aygo i ended up with two Speakers in the dash and two in the front door pocket.Nothing in the rear and the audio felt lacking. I've installed a custom set up using a JBL Gx-a602 amp and two 6x9 pioneer speakers in a custom parcel shelf in the boot. now the sound seems unbalanced like all the sound is coming from the back and the front 4 sounds like its producing nothing. would i be better off replacing all the front speakers and if so what size would fit in a 2016 Toyota Aygo dash and front door or would i be better off fiddling with the amp to try and balance the speakers out. the amp is placed where a spare wheel should be if anyone was wondering.