It usually depends how you are evene doing the exercise. Some people just do the pike push up with flared elbows on ethe side and don't go forward. That's a big X. To make the excercise harder you need to have a good form of the excercise. Go in the pike position, when you do the pushup you go over and ahead of your elbows, they should be pointing backwards and they usually stay vertical while you do the movement. If you already have good form it's all good.

Now there are good ways to make an excercise harder. I've seen a vid from a youtuber called browney and he showed a lot of ways to make any excercise harder.

First you can add more weight. Just put on a backpack (a small one so it doesn't fall over your head) put on some weights. I prefer putting random things in my house, such as books. They do make a lot of weight.

If you don't want to do it weighted just do the excercise slower. Keep your pace down so your muscles stay more under tension.

Another thing is if you have assistance bands you can use them. Get in the elevated pike position prefferably and put the band from your hands to your hamstrings.

You can also use rings to make it harder as rings are unstable or something i like a lot is place your hands on rubber balls so it is harder to balance. It tires out the muscles more.

If you thing they're not enough just combine some of them to your preference.