Yes there is a way. You can move restricted area just on server side (i've done it hard way in early 2014 by moving all points or resctricted area shape in map file on server side - but it takes hours to do without scripting and programming - Was working fine for Server version of Plantation Town map early server version: https://www.youtube.com/watch?v=_Fp5-qVzmCs).
That was actually about making the map bigger (not unlimited though) not smaller - but the same rule - I've just moved also spawn points (you can check how it works on That requires messing with map files and is not fun to do at all. Stupid way. I just had no other way that time - it was before our network even existed. Raw times of GameSpy. But I can assure you it works just on server side even without any SSM :) Can restrict areas on PS to small ones.
That way works also on IA maps.
I've done it for Armada in 2015 - moving the fight area to the deck with closing some parts with solid objects spawned by level designer on server side - to the rest of the ship and moving spawn points up. All on server side.
Here is event from 2015 done on Server Side map like that - starts after Steel Mill at 6:00 :
- Just an example what can be done on server side with classic IS map - without using editor or autodownloader. You can make smaller maps out of big ones not just by moving restricted area points.
You can also create new small maps on existing maps just on server side - here's Boxing are on Autpost. Actually - outside that map. With spawnpoints and new objects outside: https://www.youtube.com/watch?v=3yVRK8VDQ_c
Or this one made on Quarry in 2014 - outside it - No map downloading required - server side - limited area and new ideas: https://www.youtube.com/watch?v=obAiRy5MT0Q
BUT - Since we've got autodowloader 5 years now - You can also easily create your own version of Power Struggle map like Mesa and restrict Half of it - use your invention - by easily moving restricted areas just in editor. Best way even for "BestNoobs" - So players will download your version before playing - not a big deal now. This can help you to gather people in small area of huge PS maps. You can try that out in few minutes.
AND there is also the easiest way. And it's been done many, many times before. Doesn't require any skills or effort at all. They call it The "PoolDay"- way. But I'd recommend the way called "Steel Mill" or "Quarry" or "Steel Mill (PS version)". Good enough even for the fun of 4 fighters. This works pretty well. I wouldn't recommed "AimMap" way though - because in my opinion Crysis should be about freedom in open area not spending time in a prison cell 10m x 10m. But people like it anyway for some reason spending 5 hours in a row there. And that reason is not just aim training. So there are few options. Try them out.
Anyway - Good luck with your works. Have fun.