It's not uncommon for the .46 FXi to continue to break in a bit after you fly a gallon or two of fuel through it. You'll have it pretty well dialed-in where the idle is a bit fast but reliable, then you go fly it three or four times and the same idle setting will "load up" a bit. You can then turn in the low speed setting another 1/8th of a turn or so, which will result in a lower idle speed.

The basic break-in proceedures in the manuals are important for the initial run-in period. Glow engines will often have a mind of their own, and they tend to settle in when they want to settle in. Just keep your low speed needle turned in enough that you can idle the engine for 10 seconds or so without the fuel loading up so the engine dies when you go to rev it up for taxi or takeoff. Keep your high speed setting turned in so that the engine sounds like it's near peak power with the throttle wide open, but it's still rich enough that you get a steady stream of smoke coming from your exhaust.

The really nice thing about glow engines is that they tend to settle in more and more as you run them. When well maintained, a two-month old engine will run more powerfully and reliably than a two-week old engine while a two-year old engine will be more powerful and reliable than a two-month old engine. A lot of folks on these forums who have been flying for a while are still running old and reliable favorite engines that they've had for many, many years.