Yes I would cover it up and also add mulch on top to reduce erosion like that. Its probably happening from rain or when you water, it pushes the dirt around and sometimes out of the pot and eventually ur soil level decreases. You can add the soil but just be careful to not go higher than where it was originally planted. But definitely add some mulch to the top

The drop in soil level in pots mainly comes from the organic matter in the mix rotting away. In the ground worms carry organic matter from the surface down into the root zone. In pots you're not likely to get that happening. The better solution would be to repot with fresh soil mix but meantime topping up the soil level would be okay.

i push the soil down to pack it in around the roots when planting.

you cant use a lot of force, but, you should use a little.

i also always make sure the container is large enough to let it grow out for a year at least. There are a couple of other benefits to larger containers.

i leave space at the top of the soil, to the rim of the pot, so i can add mulch on top the soil. i may add a little dry grass clippings, or compost first, then, woody mulch on top.

this keeps moisture in, and the compost and mulch will break down and feed the soil..

with a larger container moisture stays more consistent as well.

as far as this plant, adding soil is fine ( i would probably use compost)

just dont let anything stay against (touching) the trunk that will be wet.

thanks for all the thoughts and advice.