I think that because they burn, they get smaller in size. If their diameter decrease when they burn, is this decrease slight (trivial) or dramatic?

It’s usually 100%

Yep. FYI: A meteorite is a meteor that has enough material left to actually strike the Earth.

Right. Most meteors (in fact, the vast majority) are small and burn up completely in the atmosphere. We are pounded with these all the time.

To give a slightly more detailed answer for the OP: This is one of those cases where exponential growth is very important.

The rate of burning up is related to the surface area of the object, and so this grows with a power of 2 as the asteroid increases in size - if you double the diameter, you quadruple the surface area. It’s probably too simplistic to say that you quadruple the rate that material burns up, but maybe we can use that for visualization purposes.

However, the total amount of material that needs to burn up is a power of 3 - double the diameter and you’ve increased volume/mass by 8 times.

So a meteor with 2x the diameter does burn up material faster (4x as fast) but it has 8x the mass to burn and so takes 2x longer to burn up. A meteor with 10x the diameter burn 100x faster, but with 1000x the mass, it takes 10x longer to burn up. At 100x the diameter, it burns 10,000x faster and has 100,000x as much mass, so it takes 100x longer to burn up entirely.

But let’s say we only have 5 units of time for burning. In this case, the 1x and 2x meteors burn up entirely, the 10x meteor loses 50% of its mass, and the 100x meteor loses only 5% of its mass.

One factor that is omitted is that meteors often fragment as they burn up, resulting in many small pieces which in turn rapidly burn up/break apart more, resulting in an explosion, as we saw the other day (the pieces that hit the ground were scattered fragments of the original meteor, not what was left of a large body slowly burning up uniformly). It’s even possible that a smaller meteor might be more likely to reach the ground without burning up than a slightly larger one, if bigger meteors are more likely to break up.

is it moving towards you or away from you?

Does angle of entry = time in atmosphere = difference in max temp the burn surface of the meteor reaches or is incoming speed more important? Or is there a cross-over point?