Since I’ve never studied the Chen Man Ching forms, I can’t really say whether we use a similar mechanism in the “tiger walks” exercise as the first leg movements there.
I can say that there is no intent in the “tiger walks” to drop the lower dantian. You just shift your weight to one side so the weight of your torso is on that leg. And you let the knee of your other leg move forward to raise the heel of that leg’s foot.
Just be sure that as you shift weight, you do not drop or lower your hips physically in any way. Don’t let your hips or legs collapse downward.
Yes, the weight of the moving leg should come to rest on the ball of its foot, putting pressure on the “bubbling well” or “bubbling brook” point there.
And as always, experiment with various ways of playing with this and find out what works best for you.
Have fun.