Oh, well that is good. Phoenix is a great sim. Load up the Trex450 and get your hovering skills up. After you master hover, even if just tail-in orientation, give the simulator some "weather"... turn up the turbulence a bit and give your self some moderate wind (5-10mph) and gusts (15-20mph). It will help you learn how a real helicopter outdoors will behave. If you want, load up a Trex250 and note how much faster it is with regards to cyclic input. If you get used to a 250 and switch back to the 450, you will be shocked by how docile the 450 will feel.
The problem with hovering a helicopter in a single spot is what we call "dirty air". Basically the main blades throw air downwards, and some of that air will loop back around for a second pass. Eventually you get a donut shaped air mass rotating and you create a down-draft that robs your helicopter of lift. This requires additional collective to overcome, and when you suddenly get clean air, the helicopter will rise. This causes an up and down bobbing motion when you are hovering close to the ground.
Also, when you get a gust of wind, the gust will partially nullify this "dirty air" effect and create what is known as translational lift. This will cause your helicopter to suddenly start climbing when a gust of wind from any direction hits it.
I used dirty air in quotes because I feel that the true definition of dirty air is what is known as vortex ring state. This happens when you have very low airspeed and descend through the rotor's own downward wash, causing a stall condition near the rotor hub and a further loss of lift which only increases descent rate and causes the effect to become amplified. This is why most helicopter pilots will land a helicopter like a plane, with forward airspeed and flaring as they near the ground. I haven't experienced this phenomena on my R/C helicopter yet, not sure if it affects small helicopters due to scale.