I've find out instead of a hexagon, a pentagon is the best starting formation. A hexagon is a valid strategy to beat normal, though.
Here is the Insane Mode walkthrough:
First build a pentagon as close to base as possible with your 5 starting towers. Build another 5 towers just in front of the original 5. Switch to armor building immediately when it is available (you have exactly 10 towers at this point). If you build armor fast enough it is possible to lose no tower by reacting on the incoming ships. You will need to reinforce at least 3 armor (I recommend 4 if you are not fast) on each outer.
Don't make explosive it is a waste of precious space.
Make a few heal but don't use them now, then switch to range upgrade when it is available. Place the range upgrade in response to the long range ships which appeared on this stage. If you placed only 3 armor on each outer, you may place two range powerup on them. You should leave the last powerup space for lightning upgrade.
Place one damage buff on each of the 5 towers on the inner ring. Buff do not stack, one of this can support 5 towers around it, that is enough. Placing more is wasteful as that only increases effect area.
Continue to make range, and build towers near your buff tower as you can.
Every tower on your side that shoots need to have the lightning upgrade (the original inner ring is optional). It essentially doubles your damage. It is also the reason why explosive shouldn't be used as that will screw up enemy ships HP that increases the number of targets thus waste more rounds.
If you are placing towers on the outer ring, make these: range, range, range, ice, lightning, capital range, range, range, range, lightning, capital
For inner ring, this is recommended: range, range, range, range, lightning, capital
If you want to upgrade the original inner ring towers (which has amplify damage), give them 3 range, lightning and capital.
Always keep an inventory of healing pack. When you have less then 3 you should build more immediately. Stay alert when capital ships or black swarm of ships appeared, repair your towers as needed.
**Survival/Awesome Mode**
The main difference is that you got all options immedately when the game start, so after you placed one armor on each outer, you can start making range upgrade immediately. This headstart makes the opening significantly easier compared to insane mode.
The first outer pentagon: armor, range, range, range, lightning, capital.
Supporting towers: range, range, range, ice, lightning, capital (must be on the outer ring) range, range, range, range, lightning, capital.
My score on Insane Mode is currently ranked #1 all time, good luck beating it...
After I failed to beat the high scores on awesome (stuck at 13~14mil score) I pull off a new strategy that worked far better then I thought, survived for 2.5 hours, beaten the score of the top two combined.
Scores rack up quickly later since the number of ships is so overwhelming. Also, once you start losing towers, the base will collapse progressively. Although, when I first lose one tower my score was already over 20mil, built even more and survived a whole hour after that.
Lightning is so ridiculous, most other powerup effects in the game are jokes compared to it. In fact I only built these to get that score:
tower heal range amplify damage lightning capital
Also built 2 bombs but they are basically useless since they can't kill capital ship directly, it is better to make heal instead. Bombs works best against a swarm of ships but these are so easily destroyed by my towers, capital ships make significantly more damage. A bomb that takes so much time to construct should destroy a capital ship if thrown directly on it in my opinion.
