Every mod I've seen that increases the outpost build radius does so by changing the Actor Value (AV) "OutpostBuildAreaRadius".  Unmodded this AV has a default value of ZERO, and there's a good reason for that:  this value is used by multiple activators and quests, which set the value to what they require.  For example, the outpost beacon sets it to 150, the house decorator panel sets it to 250 (no idea why it is that big).

This means that hard coding the AV to some arbitrary value for outposts is going to screw up everything else that needs to set and use that variable.  Basically everyone trying to do it that way is doing it wrong.

The correct method is to edit the OutpostBeaconActivator, changing the value it assigns to the AV.  This is, of course, a problem because xEdit won't copy-as-override the beacon due to reflection data.  Luckily, I build star systems

  I know a way around that problem.

This mod contains an override of the beacon itself, which sets the build radius AV to 300, double the normal size.  All my tests so far show this to be stable, and there are no issues building with the overhead view.  And it does not interfere with anything else that needs to set OutpostBuildAreaRadius to some other value.

I do recommend backing up your save before installing this, of course, just in case it breaks an outpost.  My current belief is that issues with other mods have been due to editing the AV directly, forcing it to be the wrong size (say, 500 when something needs it to be 250), rather than having the beacon set that value, but of course I can't test every situation.

Edit:  Gave this some additional thought.  So a mod sets the AV to say 300.  The outpost beacon then tries to set it to 150 (the default).  Conflict ensues.  This would explain the failure in placing things using the overhead view, or having to place harvesters inside the vanilla radius and then move them out to the new radius.  The beacon is fighting the AV override.  But override the beacon itself, as I've done here, and that conflict goes away because the beacon and AV will always agree.