Your input is greatly appreciated mate. Especially given how familiar (and insanely skilled) you are with the game. I especially like your suggestion of having one rate at which the speed increases from level 1 to 7, and then have a different (faster) rate after level 7 which will ramp up the speed much quicker.
I've updated the dev build so you can try it out. I've increased the speed between level 1 and 7 so that by the time you get to level 7 it's a little faster than it was in the previous build. I've also made the rate of the player's shots faster to balance out the increase in the speed for novice players. After level 7, you should notice the enemy attack speed increase a lot quicker with each level since I can now set a different rate from that of level 1 to 7. Just let me if you think the speed in the levels after level 7 ramps up enough, or if I should increase the rate some more. Should be lot easier to increase the rate now if needed since it won't affect the speed for levels 1 to 7.
I didn't change anything specific to fix the issue where sharks in the left and right channel sometimes don't attack upwards, but I didn't get it while testing the latest changes. Perhaps I changed something inadvertently with the latest updates, or maybe it still happens but I just didn't notice. Let me know if you still find some sharks don't attack upward when they should.
If all goes well I'm hoping to release Shark Attack on Monday.