I believe, rather than having designated tiles with fixed pokemon level it would be nice if all the travelling tile may spawn any level pokemon within a range (say 5 to 30) . The tiles should have fixed pokemon types and the level may remain variable.
For making distant tiles more attractive, it may be done that each pokemon should have a number as it's rarity rating, similarly the tiles may have potential ratings (i.e. pokemon upto that rarity rating may appear there). The amount of appearance can also be implemented by applying an exponential function onto the rarity rating (so the lesser rating pokemon will be in abundance and higher rated pokemon may not appear even once for 100 of common rarity rated pokemons).
Hope my suggestions make some sense
Waiting for the feedback
For making distant tiles more attractive, it may be done that each pokemon should have a number as it's rarity rating, similarly the tiles may have potential ratings (i.e. pokemon upto that rarity rating may appear there). The amount of appearance can also be implemented by applying an exponential function onto the rarity rating (so the lesser rating pokemon will be in abundance and higher rated pokemon may not appear even once for 100 of common rarity rated pokemons).
Hope my suggestions make some sense
Waiting for the feedback