If you know a little bit of javascript you should be able to adjust the code within the Ritter.canSpawnOn function in the plugin code.
it's a pretty straightforward function and easy to add to or remove things from.
Ritter.canSpawnOn = function(x, y, regions) {
var region = $gameMap.regionId(x,y);
//if ($gameMap.eventsXy(x, y).length > 0) return false;
//if ($gamePlayer.x == x && $gamePlayer.y == y) return false;
if (regions && !regions.contains(region)) return false;
if (!$gameMap.isPassable(x,y)) return false;
return true;
};
So if you wanted to spawn on top of the player and on top of other events you can simply comment out the two lines as shown above, but if you wanted more control you can expand on the if statements and set more conditions as well.
This is indeed expected behavior as a basic canSpawnOn function, but I left it very easy to edit, just return true if the spawner can spawn on the tile or false if not. The function is structured so it will first attempt to return false but if it passes all the conditions it'll return true at the bottom.
I hope this helps, and if you need further help be sure to ask!