No, the speaker locations haven't changed (from the OP's post, it seems that he replaced the dash speakers and put the new ones in the original locations), and I would be shocked if he didn't put them in the same holes. I would assume, maybe incorrectly, that the replacements are a matched pair, so I don't see why just plopping in new speakers would result in an imbalance as the OP is having, since the right one should increase in volume too. The only way I would see that happening is if the tweeters are adjustable as far as angle goes and the left one's output is bouncing off the glass directly at the driver's ear. I've been in a lot of cars with half assed car stereo installs over the years and never seen any major imbalance after a speaker swap that wasn't able to be diagnosed as a bad speaker or wiring/amp issue. A lot of these installs were comically bad. My favorite was a friend's brother who "installed" 6X9" speakers by simply setting them on the rear deck, not seeming to realize they would become missiles in a wreck. He was lucky, when it flew, it missed his head and just went through the windshield. The speakers being ruined was the least of his problems. His really nice '71 Chevelle SS was gone.
On my car, a 2010 Challenger with the "Sound Group II"Boston Acoustic 7 speakers and sub, the back speakers do so little I didn't bother changing them. My friend spent a couple of hundred bucks on the rears to swap them to JL's and the slight improvement was really only audible when you had the fader set "wrong" and the back speakers were way louder than the front, which sounded pretty bad. I took some of that money and put some sound deadener sheets in the doors to quiet down road noise, and a little in the dash to quiet the buzzing it gets in the colder months until the car warms up inside. My friend and I kind of take turns being guinea pigs with mods and stuff. I was the first one with the dash speaker swap, he was the first with the rears. The results, or lack of them, made me pass on doing it. Most of the time, going back 3 vehicles what one does, the other one does too.