I thought leaving solid back row pins mean the ball is getting into its roll too fast(or am I thinking too slow? I'm just learning this myself) and it's a tad high in the pocket. If that's the case, it seems like the adjustment you'd want to make would be to change your breakpoint a little further outside I think.
Please correct me if I made any wrong assumptions here because I'd really like to improve my carry percentage as well.
This is a little to generalized a statement to be completely true, as there are many reasons for leaving back row pins, and each pin is different (and some have multiple reasons). The "language" of the pin fall is what will tell you what your adjustment needs to be. The reason I say this is because the adjustment to get rid of a 7 pin all depends on what the other pins in the rack did to leave it. If you see that the 5 pin is passing the 7 in front, that means that your entry angle is not sharp enough, or it could also be that the ball is deflecting due to either beginning its roll to late, or it could also begin roll to early and burn up. Therefore there are other keys to look at. What is the headpin doing? What about the 10, how does it fall? These all "tell" you what to do, but you have to be able to interperate them just like learning a new language. If the headpin flies into the wall and comes in front of the 7 as a messenger, that means the ball is rolling at the right time but the entry angle needs to be increased (on most occasions). This flat 10 look with a weak entry angle can also leave you with that infamous pocket 7-10 as the ball is hitting the headpin first, and going more head on into the 3, causing the ball to also clip the 6 in most cases (the the 3 just barely catching in on the left of the 6) and pushing the 6 into the gutter and not into the wall and belly of the 10.
It would be most benificial to find a coach, or someone with a great deal
of knowledge (not everyone that has a high average actually knows what they are talking about) and have them help you intereperate what the pins are trying to tell you. These clues will help your average increase very quickly, as you can start adjusting before you leave pins. Its always nice to adjust on a strike and put 10 in the pit on the next ball, without having a spare in between. Good Luck!