Striders spawn on the bottom of the lava lakes

Striders are supposed to stride accross lava surface and not at the bottom of the lava lakes.

Steps to Reproduce:

1. Go above a lava lake
2. Run the command /fill ~20 32 ~20 ~-20 16 ~-20 air 0 replace lava
3. Repeat the step above in a few areas above lava lakes

Observed Results:
You will see striders existing/spawning below the lava lakes and not in the surface, making striders look like spawing very very unfrequently.

Expected Results:
Striders should spawn in the lava surface and not in the lake's floor.

Screenshots/Videos attached: Photos and videos describe the issue better