If you don't have any acoustic treatment, I'm with you that an 8-inch cone is probably too big. I have the KRK Rokit 6s and I think they function very well, and in some ways prevent me from going too loud with my music.
I don't have any experience with JBL speakers outside of what my school has, but to be honest as long as you spend enough time referencing other music on your monitors you'll start to learn the particular idiosyncrasies for that referencing position, and use that to compensate. If you're really really stuck, put your favorite reference track into your DAW, open up an EQ, and change the frequency response until it sounds like you think it's supposed to sound normally. Slap that EQ on your master chain, then turn it off before bouncing your projects and see if it's giving you a more accurate result than without using a compensation EQ.
