Now you've stumbled upon the best kept secret in RC. Yes, the A-D converter circutry may have 10 bits of resolution, but the joystick pots are tied to +V and Ground, and there are no divider network before the wiper voltage is presented to the microprocessor's A-D converter. You are absolutely correct that the joystick only rotates the pot approximately 90 degrees out of the pot's 270 degree rotation. The microprocessor's A-D codes ground as zero, +V as 1023. Therefore, the actual A-D numbers being used for the extremes of the joystick are nominally 341 to 683, with 512 as the center. If the pot is mounted slightly out of center, then those numbers will shift accordingly. The actual values for each extreme are determined during the joystick calibrate process, and the center value is the midpoint between the two extreme values.
You don't have to take my word for it, you can look for yourself. Here is the schematic from the FCC website as part of their FCC Type Acceptance filing for the FlySky CT-6A. You will note that the joystick pots are tied directly to +5 and Ground, and the wiper is presented directly to one of the 8 A-D converter channels of the STC12C5410AD microprocessor, which has 10 bit A-Ds:
https://gullfoss2.fcc.gov/prod/oet/form ... or_pdf=pdfPerhaps Hitec does use all 10 bits of the A-D to code just the middle 90 degrees of pot rotation, I don't know. However, I do know for a fact that none of the FlySky products; the 4 channel, 6 channel, or 8(9) channel 9X do on their four joystick pots. (They do, ironically, use all 1024 counts on the VR knobs, since they do rotate the entire 270 degrees, making them more precise than the joysticks!) All of those radios have their schematics on the FCC website, and can be found if you search the FCC ID number at the FCC website.
They may use 10 bit internal calulations to take the raw A-D number from a pot, factor in the digital trim number, factor in the programmed endpoint percentage, factor in exponential rate, then generate a 0 to 1024 count to send to the receiver as a servo position, but the FlySky radios do not use all 1024 counts from joystick min to joystick max.
I think a return phone call to Hitec would be in order, and a schematic would tell all. However, I will bet you a $20 USD donation to your fantastic RC Model Reviews site that they won't release the schematics. I'll double it to $40 USD if they do release the schematics, and it does turn out that they condtion the joystick pot signals so that the 90 degrees of rotation are coded in a full 0 to 1023 count, or something very close.
Edit: Another possibility is that 12 bit A-Ds are very common. If Hitec used 12 bit rather than 10 bit A-Ds, then the middle 90 degrees of joystick pot rotation would code to a minimum count of nominally 1365, a maximum count of 2730, with a 2048 for joystick center. That would give you 1365 counts to code the entire joystick range, more than enough to meet the ultimate 1024 count resolution. However, the same joystick calibration proceedure would be done to determine the actual joystick end counts, which would vary from radio to radio. Any "deadband" near a joystick extreme would be eliminated by a recalibration proceedure.
John