At the moment, setting Collective (Analogue) is very unintuitive as the natural inclination is to set Collective Raise (Analogue) to the direction/half of the throttle you want to use to increase Collective (i.e. Z Axis +) and Collective Lower (Analogue) to the other direction/half (Z Axis -).
However, as tuplas explains at the end of this ticket http://feedback.arma3.com/view.php?id=2015
"The engine only starts with up collective which starts at 50% if you have both the raise and lower collective assigned to different parts of the axis.
If you want to use 100% of the slider range for up collective you can do so by assigning both the - and + range of the slider axis to 'collective raise' and nothing to 'collective lower'. You will lose some descent speed by doing this though. But it'll start the engines even at 1%.
You'll get 75% for up collective and 25% down by assigning both the - and + range to 'collective raise' and only + or - to 'collective lower', depending which way you use the throttle. This will not decrease the descent speed.
Keep in mind the order in which the - and + ranges are listed in the controls affects the direction in which the throttle functions."
This last point is relevant too as it makes setting the Throttle up in the desired direction awkward.
Even coming from ArmA2, where I'd learnt about this quirk at some point and had my Collective (analogue) set correctly, I still forgot and was confused by A3's Control settings and set it wrong again, so it's clearly not obvious.
What would make it more user-friendly is to have a single Collective (analogue) setting, which would be assigned to the desired Axis (i.e. Z) regardless of + or - and then a simple "Invert" checkbox somewhere to reverse the direction of the Collective as desired (ideally this should be a separate setting for helos and planes as I like to pull it towards me to increase when flying helos to simulate a Collective but push it away to increase when flying planes, like a throttle).
To acheive the 75% increase, 25% decrease range tuplas describes, this should be adjustable with a simple Balance slider, probably separate from the Sensitivity one, so that in the middle (Default) it would be 50/50, with neutral/50% in the middle.