Whether you like it or not, colossals are a regular part of the game that you have to accept. Unless you make a house ruling not to play them... but back to my point...

Since walls/indoor blocking is the only thing that can block LoF to colossals, do you find it best to pick an indoor map that provides cover, or do you want wide open spaces of an outdoor map for easy pew pewing and charging? What if you're playing against them? Guess it's highly relative to you're teams strengths and weaknesses.

By random chance I prevented colossal relation the other day due to crowding around lots of walls. Is this an anti-colossal tactic worth focusing on?

I generally prefer to use indoor maps unless I'm Stealth-heavy. I love Lord Chaos Master Order as an indoor mobile barrier, taking the hits for my team and regenerating endlessly.

Yes, that is one reason why the ROC Underground Tunnels and STAT:OS Underground Cavern maps are so popular. At one point, the STAT:OS Underground Cavern was going for $30+ on the 'Bay; made me wish I would have gotten a few more on Release Day ….

You can also simulate this effect w/ Barrier to help protect from CR. TMT Sersi, EAX Ezekiel Sims, and others with Free Action Barrier are particularly effective in narrowing-down potential landing zones for the .