How do I shorten macaron feet? (French macarons)

Recipe for reference:
3.5oz gran sugar
4oz egg whites
4oz almond flour
7oz powdered sugar
Tiny bit of cream of tartar

1. Make meringue with stiff peaks
2. Fold meringue into the almond flour/powdered sugar mix 1/3 at a time
3. Pipe and bake at 300F for 15min

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I feel like I’m getting the hang of making macarons now. Though, every time I make them, the feet turn out a bit tall and the inside is relatively hollow.

I’m not necessarily upset at the results because they taste good. Though, I am curious about what I can do to not have them be hollow.

(Also, I accidentally splashed water onto some of the macarons from the sink. That’s why one of them looks a bit wet.)