I have a Poco. Firstly, what is a lid? I suppose I have it somewhere. The angle of repose of my anthracite seems to be about 30% so I cut out a piece of crap steel and used aluminium pop rivets to make a triangle and placed them in the bottom corners of the hopper, loose fit for easy removal and if some coal gets jammed there so what. - the coal never flows from there anyway. So perhaps my hopper is now 180#. I was thinking making a hopper extension on the top to bring it back to 200# usable or even more. Sadly, the pizza guy arrived and I had some Blue Moon in the fridge and even an orange so that was that end of that idea. Without the lid it does not have to be an exact science. Never did part two of the project as I was way too lazy and the existing hopper lasts long enough as it is even on the coldest day. Oh well, story of my life.
Same here with my Poker, agree that side wedges would likely cure the center drop "angular repose" on just about any stove.
In past years there have been discussions on the forum (not just LL stoves) about this issue and some have suggested some sort of barbecue motor spit that rotates ocassionally tickle the side coal into the center....or betterIMO try the side wedges..the wedges can even be made of wood so that they can be removed, etc...I'd just make sure they were in some way lightly attached to the box so they will not move around.