In one of my (unreleased) mods I changed the basic pipe-to-ground distance to 21 from 10.
I used the following in data-final-fixes.lua:
data.raw["pipe-to-ground"]["pipe-to-ground"].fluid_box.pipe_connections[2].max_underground_distance = 21

It does increase to 21 but your mod acts like the distance didn't change and shows the distance as 10 instead of 21.
To test your mod, I commented this line out in my mod and changed the value directly in base. (entities.lua)
Your mod works fine in this case.
I also modded the underground belts directly, and your mod shows the change correctly. It is strange that doing this for belts works but for pipes does not.

I don't think it is your mod. It appears underground belts and underground pipes are handled differently when it comes to the distance value.

Any idea how I could make my mod compatible with yours (without modifying base code) ?
I tried forcing my mod last and then my mod first in load order but neither made a difference.
I must be doing something wrong.

If you don't know what the problem is I can ask for help in the modding forums. Don't spend too much time on this on my account.
Thanks for looking at this.

I think I know what is happening. I'll try and put a release out later today.

Try it out now and see if it fixes it. You may need to figure out a way to load your changes before mine. I use just data.lua so it loads in the first stage. If your mod is alphabetically before mine it may work out of the box. Not sure though.

I am really sorry. I posted this for the wrong mod. It should have been posted on the show-max-underground-distance mod. I am an idiot.
Sorry for wasting your time.

haha, it's all good. I had forgot to make a change in the pipe distance where it uses math to change it instead. I added that after I found out boblogistics allows changing the base range of belts and pipes, so after that I change it to scale with changes like that.

Cool. I tested again with your mod with a new test save and everything looks good.
Thanks again.