Is your horse actually lazy, or are they stiff, heavy on the forehand, and have learned to shut out your aids?
Is your horse actually forward and hot, or are they nervous, off balance, over stimulated and frustrated?
True impulsion to me means directable energy. If you have energy you can’t control, you don’t have impulsion, you have worry.
Being “in front of the leg” to me means that the horse’s front legs are literally in front of yours. If their forehand is tight, their front legs will take stiff, quick choppy steps beneath them, as opposed to out in front of them.
If your horse isn’t forward, chasing them with driving aids will only create more tense, choppy steps, but will not fix the problem. There is a big difference between faster, and with more impulsion.
Often we look at the forward and slow types of horses as different, but they both are showing symptoms of the same problem: stiffness and lack of balance. Both horses can be helped with suppling the shoulders, lengthening and straightening the neck, and developing a swing through the back.