flexibility for straddle

I'm unable to get a good straddle. What is causing this and how can I improve my flexibility in this regard?

So far I've been lying on the floor with my legs straight, straddled and up against a wall (my butt is near where the wall and floor meet).

That sounds like I have heard been called a gravity split. Thing is, I'm sure there is more pressue when doing a split from a stand than from lying on your back due to your body's weight putting pressure on the stretch.

Leg swings, hip extensions besides knee lunges and side lunge squats are a good start besides just working on stretching in general. Start sitting in a straddle position and holding it. Perhaps 1x or 2x a week and ramp up from there.