I had the same issue with not retaining length. I had to make changes and leave time between my installs. Honestly I had to switch to wearing wigs that i made for myself. With combs so I can take them off and treat my hair nightly. I do protein treatments now and moisture treatments.
Just remember everyone hair grows differently, my hair does not do well when i do installs at all. Since switching back to wigs over the last four months my hair has gone from ear length to just below collar bone. I have tracking pictures to prove it.
You have to find out what works for you.