Run your strides with the footstrike that comes naturally at that pace (typically forefoot).

Don't try to change your footstrike for distance runs. Running is a natural motion for humans and we each find our efficiency naturally. As you get faster, you may see your running form evolve slightly as your fitness/body adapt. Take a look at Alistair Brownlee and Lionel Sanders; their form is radically different, but both are fast runners.

Sanders running (check it out at 40:00)


Alistair running (check it out at 10:25)

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Replying
... not because I am an expert
... but because I am decompressing from work
... and full of nonsense and vim

This: Should I keep running with whatever form feels natural for the pace?

Emphasis on the natural
Don´t force it too much

Recognize that there will be an evolution
She said, you won´t be the same runner after a summer of strides

Let the pace teach you the most efficient movement
He said, let the song teach you the dance

Good running technique is not a cage to put yourself in
We do not recommend trying to adopt a certain form

Instead, run different paces in different circumstances
Pay attention to yourself and try to be disinhibited

Good running technique is a convergence
Of similar motions by similar runners

I don´t think it is a recipe, but running
Can be complicated and we all deserve help

So if I have specific advice about footstrike
It would be this: Think about turnover and posture instead

Best wishes
And sorry to be a self-centered ass

Titanflexr gave you better advice
Do what she/he says, ignore me

Thank you, both of you. Your advice is encouraging, helpful and you don't contradict each other, which makes it easy to follow!

I try to land on my feet while they are under my body and not out in front. I always heel-strike while doing it.

Listen to the posts above, be super careful when making conscious changes to your running form. You are likely to hurt yourself.

When doing strides, don't think about pace or distance. Don't look at your watch. Try this:

1. Take note of where you are starting. A perfect place is a gentle downhill in short grass.
2. Slowly accelerate to almost top speed.
3. Count 25 steps with your right foot and then stop. Notice where you are when you stop.
4. Walk back to the start and repeat. This time you don't need to count since you know your stopping place.

They absolute most key thing in running is being relaxed, especially at speed. If you can stay relaxed at fast paces the form will necessarily be there.

I don't disagree with this. But, IMO strides should be fast enough to get you off your heels. I'd say ignore the literal pace and run them fast enough to be up on the balls of your feet but focus on being relaxed. I tell people to think about being "quick and light" instead of running fast or hard. Just accelerate, hold peak pace for 8-10sec and coast back down.