Thanks for the feedback. First some data about the current decay rate:
A stone wall now turns into Ancient stone wall slower than before. The expected average (EA) is 24 hours.
Stone Wall -> Ancient Stone Wall, EA = 1 day
Ancient Stone Wall -> 1st decay state, EA = 3 days
1st decay state -> 2nd decay state, EA = 2 days
2nd decay state -> Crumbled Stone Wall, EA = 1 day
So the total EA for a Stone Wall to decay is 7 days. This is 10,000 years in game time.
The decay is happening randomly though. For every quarter of an EA time, there is a 25% chance that a wall decays one step. This means that the decay can happen either faster or slower than the EA, for individual tiles.
Now your specific question:
If you set the Decay factor on your private server to be slower, the EA will increase with that factor. Is this not enough to achieve what you are looking for? Could you tell me why you think it’s better to use the map clean-up parameter instead of the decay parameter?