It is not usual RTS. More features means more things to deal with simultaneosly and more enemies. For example the storm appears from time to time and deals damage to units in some areas. In larger maps some new enemies appear specific for the map. Larger maps are more difficult because the game has some relations with tower defence and this means the enemy may become strong. Unit production requires more place so in small map is almost impossible to build all factories and building types except when the player controls 2/3 or more of the map. The same is valid for the enemy. In larger maps the enemy could build few types of infantry, tanks, ships, submarines, planes, long distance rockets, spies, and to use specific terrain options. In smaller maps the enemy can build few of them and eventually no ships, no spies, less terrain options.
If I make a comparison with the chess, imagine that you play:
- 4x4 table with 5-6 units including 3 types of units;
- 5x5 table with 6-7 units including 4 types of units; the horse is available;
- 6x6 table with 7- 8 and the queen is presented, when your unit reaches the end of the table you can replace it with anything...
There is a difference - in the chess you know the rules and figures, in my RTS some features are new in some maps, it is somekind of campain like and TD, more enemy types will attack you.
Sure enemy weaves and types could be controlled but larger maps with more features to deal with will make it difficult anyway. The problem is when the player become good small maps with less features (well known already) will be too easy and the difficulty could be controlled by other things. Maybe I should combine them.