Following your ranged weapon example: Imagine (going with RPG stereotypes) that I have a Goblin, an ogre, and a giant in the same tile. I am shooting at them with a bow and arrow. Because of the giant's size, I am more likely to hit it, and the ogre is the next likely, with the Goblin being hardest because it is the smallest. In this way, it could become a strategy of the game to use larger characters to tank for the smaller ones. Maybe there is a drawback to this: For every larger character they share a space with, movement speed (in number of tiles per turn) is reduced by 1. So, the goblin will be set back 2 move speed, the ogre one, and the giant will be free to move unimpeded. Or maybe they line up in the order they get there. IF the giant moves north to a tile, it will face North. Then if the Goblin shows up by moving North, it will be behind the giant. Since the giant is taller, ranged weapons may not hit it. In this same manner, if the Goblin showed up followed by the ogre and then the giant, any one of these may be targeted. Also, if the giant is north of the goblin on the same tile, the goblin may be attacked from the East, West, or South.
Or it could be something completely different. A rogue class that gains attack bonuses with short weapons when sharing the same tile set with an enemy, but loses access to longswords and the like due to the close range. Or an archer who can only use his boot weapon in the same tile. A mage who must share a tile set with an ally to cast a protective shield.
Very very interesting examples.
It is very easy to maintain a list of things in the tile. E.g. "Giant,Ogre,Goblin" arranged in order of who arrived first. Then, instead of clicking on or scrolling through the small icons, players can just easily fire at the entire tile by clicking on it. The person in front will have a higher probability of being hit by the projectile depending on size (goblin in front has much lower chances).
Mages can cast "shield tile" which cause him to take all attacks with 100% probability, but he will have temporary X hp to withstand this onslaught before his actual hp gets damaged. Thieves can "backstab" with a dagger if they managed to be "behind" someone on the list.
Oh wow we opened up quite a bit of design space!! I am going to have SO MUCH fun with this. Thanks a million!
What do you mean by "tile-locked"?
An important thing to consider is whether the characters are tile-locked. If they aren't, you can do just fine by not allowing them to get too close to each other. If they are, my last paragraph applies.
It depends on the size of the tile. If one tile is about the size of the average building, go ahead. But if one tile is one meter by one meter big, you should only have 1 character on each tile.Each tile will roughly represent 1 room. Some huge rooms and corridors might be made up of multiple tiles. (you probably noticed that this system has its roots in MUDs - Multi-User Dungeons)
I chose to do it this way because the usual tile system is very art asset intensive. I would need a lot of art to tile one room. In my case, I just use 1 drawing to represent the entire room (one man hobbyist indie development team with small budget sorry ). Also, I don't want players to grief by blocking up corridors and entrances physically.