The Mavic gets to 11000 or 12000ft then loses signal on the same open rural corn field flying conditions
3.3 to 3.6km ?
The difference can be related to all sorts of factors, as mentioned altitude is the main one . . . if you were high, antennas pointed correctly, good LOS between controller and MP, then there may be other things coming into play, even the weather / atmospheric conditions can affect range from day to day.
There are many flight records posts on MavicPilots forum, it can do it but likely not consistently.
Not into it myself, but can see why rural users might be for checking property at distance etc.
Bearing in mind VLOS rules in most countries, I usually keep it pretty close, up to a km
once (3300' or so), but in general around 500m (1640').
I'm getting Firehouse Tech ArcIIs for the MP, which will be detachable to fit to the Spark too, using good urethaned velcro tabs strategically stuck on the legs . . . these will allow me to fly somewhat further VLOS, but the spirit of the VLOS rules is usually so you can see any risk close to your drone, and be able to take evasive action (land or change altitude quickly).
If too far away, you don't have the correct perception to do this, and using the camera is very lucky to see what's around and what needs to happen in event of airspace.
The Mavic flight time is all over the Spark though, I routinely get 25 mins from my MP, landing with decent %
battery still, the Spark usually 15 mins.
But like flying the Spark for sure, a bit noisy, but ok where I fly normally.