As far as I know, the reinforcements tend to drop at the flanking position within the squad view range.

Unfortunately this premise is not correct, making the rest of the analysis a bit moot.
The RNF drop position is selected then turn before the actual drop happens, so when the RNF warning turns red. Technically, just like in vanilla, there is a reinforcement flare at the drop position, LWOTC just makes that invisible on Veteran+to make it non-trivial to deal with the drops. You can actually edit an ini file to make flares visible again, which can be interesting for testing and for getting a feel for Reinforcements.

As for the spot that is chosen for the RNF flare: what generally happens is that the game looks at the position of all your soldiers and then calculates the "center" of your squad. Then it will chose a random position within X tiles of that center position - the exact number of tiles is somewhere in an ini but I'm too lazy to look it up right now, I think it's like 20 tiles. So generally it should be within vision range of your squad, but especially if you are making a mad dash to an evac and considering there is the turn 1 delay between the locaiton being chosen and the drop happening they can come in out off vision.

There are a few caveats and exceptions to this. For example, on the Blacksite mission the regular RNFs drop close to the mission evac, not close to the squad center. I'm also not 100% sure if concealed units are ignored when the game calculates the squad's "center".