According to boards.txt shipped with the Arduino IDE the following fuse bits are used for Arduino Nano boards:
nano.menu.cpu.atmega328.bootloader.low_fuses=0xFF
nano.menu.cpu.atmega328.bootloader.high_fuses=0xDA
nano.menu.cpu.atmega328.bootloader.extended_fuses=0x05
What makes you say that full swing crystal oscillator setting is necessary or appropriate? The datasheet for that resonator doesn't seem to suggest that full swing is needed.
Per datasheet, "This is useful for driving other clock inputs and in noisy environments". I don't think either of those are true under typical arduino conditions, so using the normal low power crystal options is fine (and indeed, it is, as evidenced by the huge number of nano and clone nanos in use with those fuse settings).
Atmel seems to be deprecating the use of full swing crystal clock option, generally - it's been removed from the 328pb, for example.
After my opinion there is a huge difference between a crystal resonator (which is a passive component) and a crystal oscillator (which is an active component). The use of these two sources of clock is different as well:
1- Crystal resonator (mounted on Nano): XTAL1, XTAL2 are connected and together with oscillation capacitors and internal circuitry clock is generated.
2- External crystal oscillator: Only XTAL1 is connected. No need for capacitors or internal circuitry, since the crystal itself generates the clock.
It's a bit suspicious that Nano circuit works fine with the latter, though the hardware suggests the first.
there is a huge difference between a crystal resonator (which is a passive component) and a crystal oscillator (which is an active component).
Yes, but the fuse setting you're complaining about is NOT for an external Crystal Oscillator; it's for an external Passive Crystal using oscillator circuitry internal to the AVR.
For an active external oscillator, the low nibble of the low fuse would be 0, rather than 0xF or 0x6.
