...Should I consider a range extender or give it a miss? Would that just increase the line of sight and do nothing for obstacles in the way?
If anything it will only increase the LOS distance, not so much when it comes to penetration through obstacles.
Can also add in a bit more regarding radio transmission & what to think about, besides a straight unobstructed line between the controller & the drone. This below, can also be a real source to interference if flying (having the LOS) close in between obstacles.
Below describes the Fresnel zone ...
A wireless LOS is best defined with the concept of “Fresnel Zone”, not a straight line, where the LOS actually is a ellipsoid area that is required to be at least 60% clear of any obstruction to ensure the highest performance of wireless link. Typically, 20% Fresnel Zone blockage introduces little signal loss. Beyond 40% blockage, signal loss will become significant.
The formula for determining the radius of the widest point of the Fresnel zone is:
So flying at a distance of 1000m, the radius of the Fresnel zone is 5,6m at the widest point (half way) if using 2,4GHz... or 3,9m if using 5GHz.