from my understanding in car audio you want the rear for a filler, some people dont run rear speakers at all. here is a quote from an article i have read to help me set up my stuff and save me some money by getting "cheaper" speakers in the rear. i still have type-r's but i got the coaxils and sold the components i had originally put back there. im just glad i didnt drill holes in the back like i did the front
Adjusting for rear fill
Once you have your front speakers installed to your liking, you'll want to make sure that your rear speakers are doing their part to create an ideal soundstage. While personal taste plays a role here, most experts agree that you should adjust the volume level for rear speakers so that you're barely conscious of their presence.
While your front speakers should give you the best midrange and high frequencies possible, your rear speakers can be conventional coaxials or low frequency drivers. Their purpose is to add ambiance and depth to your forward soundstage. If they reveal too much high frequency information, they'll "pull" the stereo image to the rear of your vehicle, away from where you want it.
and here is the whole article
How to Get the Best Stereo Imaging & Soundstage