@Trulux Three things i do to get the most parking spaces filled up.
Vehicle edits need to be done to increase the chances of having a car parked. Example if one car is already on the road, it wont spawn another in the parking space. I use my vehicle template oiv to make all cars spawn the same rate and increase chances of seeing.
Second thing i do is modify the popcycle file to always spawn the max amount of parked cars. My enhanced population mod has a modified popcycle file.
Third would be using a gameconfig made for heavy traffic spawns, I use the heavy option in my gameconfig.
Combining all three of those mods creates the most amount of parked cars I have seen.