Welcome to CoffeeSnobs!
The Ikon does not have a pressure relief system, so if you pull the group handle off within a minute or so the water and grounds will squirt, and the puck will be wet and soggy. I generally leave the handle on until Ive steamed the milk, and cleaned up everything else, and sometimes still get grounds stuck to the shower screen.
The shower screen is also quite high and Ive found that the best dose (after tamping) is only a couple of mm below the rim of the basket.
If you are getting shots finished in 15 seconds then the grind needs to be finer or the tamp harder. The time starts from button push and includes the 4 or 5 second pre-extraction phase.
I dont have any experience with the 480 but someone who does will be along soon.
Keep varying one thing at a time--the Ikon will make pretty good coffee.