I found this article very helpful to explain hamsters territorial behaviours
Peeing on the hoard is when they think a predator may be around who might steal it (ie you possibly - lol). Although sometimes I've found they hoard in their potty when they've run out of space under the nest as well. I resolved this eventually with our last hamster. I tried moving his potty but that didn't work - he just kept peeing in the same place and ignoring the potty. I then changed his house for a bigger one, with the potty inside the house - he had more space for hoards and his pee area and that did the trick. He would only hoard in his potty then if his main hoard had got very big.
Moving the hoard next to the potty, as you are doing, may also work as well - it's a difficult one as it can become an itch scratch cycle - you have to bin the pee'd on hoard with the potty contents so it makes them want to pee on it more. When you empty the potty you could put a pile of new food somewhere very close to the potty and let your hammy see you do it. After a few times it might work.
Anyway have a read of this - it covers all territorial behaviours. Their nest and hoard are intensively guarded. Best not to do big clean outs regularly. With enough depth of substrate, you can just spot clean occasionally and only need to change the substrate every 6 to 8 weeks or even longer. Even then I only change about half of it and replace the dry half or bottom half and mix it in with the new so it still smells familiar. Also don't clean everything at the same time. Do the wheel a different week and the toys a different week again. Toys often don't need much cleaning or very often. And if your hammy uses his potty his cage should mostly stay clean anyway. Also there is no need to use disinfectant (except in cases of illness or disease) - a warm cloth would do for the cage base. Which is usually clean and dry anyway with deeper substrate.
What I used to do with the pee'd on hoard in the potty was try and save a couple of bits that aren't too bad (even if a bit whiffy and put them on top of the pile of new food next to the potty, so they get the message lol. Also sometimes you will find that something extra special is put in the potty because it's really important
So try and save that or replace it with something identical next to the potty. It can take a bit of patience!
Syrian hamster behaviour