I've been working hard to master the L-sit, and despite my hard work, my progress has been slower than I'd like.
I discovered a reddit thread that shed some invaluable light on my posterior chain weakness. A pilates instructor was explaining the importance of lifting from the glutes and hamstrings in the L-sit and not just from the core. He/she gave an excellent exercise to strengthen the posterior chain called the reverse plank (also called the fish pose).
I tried it and found it to be quite challenging. In fact, I could barely lift a leg during it. My posterior chain is definitely a weak spot and I'm excited to strengthen it.
I plan to practice it over the next mesocycle so I can see if it helps me achieve greater lift in my L-sit.
You can see my video explaining and demonstrating the exercise here: