If I understand your original question, you are looking for increases in muscle size, but you want to increase muscle size via a different method than simply using heavier weights. Is that correct?
In simple terms, for progression there has to be either an increase in weight moved or an increase in the number of reps performed. This is directly related to force x distance = work performed. A simplified example: say you move 200 lbs for a distance of 3 feet for 15 reps. Work performed would be 200 x (3 x 15) = 9,000. Using 180 lbs for 20 reps of the same distance is 180 x (3 x 20) = 10,800. More work was performed with the lesser weight. This is where the time under tension principle takes effect. Since more work is performed with 180 for 20 reps, the muscle is damaged/stimulated more, and providing proper nutrition and recovery time, it will grow more.
The key here is not to immediately increase weight. The more reps performed, the more work done and the more muscle stimulation occurs. What you want to do is to try to increase reps using any particular weight. Only once you have attained a "threshold" number of reps that you can perform easily of your own choosing, then increase the weight heavy enough to perform a minimum number of reps, possibly in the 6-10 range or some other number of your choosing (technically, the 6-10 range is only a guideline and you should do what feels best to you). Then you start working on increasing the number of reps again.
I always used to try to increase the weight each time in earlier years, and I got pretty strong, but I didn't build the size along with it like I perceived other guys doing. Only in the last year have I finally figured out that I need to focus on reps first, my own range going as high as 25-30 on some lesser exercises and 15-20 in the core exercises (such as squats, etc.) I have literally had to retrain the way I do these exercises as a result, and suddenly, I'm making far more progress in terms of muscle size in a shorter time span, especially my legs. It's extremely satisfying to be able to add 1/2 of an inch to your legs in 3 weeks, which is what happened when I first figured it out with squats this year. I still do DC, but I do it building up to a higher number of reps since that is what MY body needs.
