inverse-square?
a microwave beam can travel hundreds of miles and still be pretty focussed - that's why they are used as point2point links
reflection is another issue.
Nope!
The signal from a dish antenna as used in point to point links is not really "focused".
It starts out as a point source, is reflected by the dish and ends up a wavefront which appears to come from all parts of the dish.
It is easiest to describe this using the tools of Classical Optics, showing the signal path inside the dish and beyond as individual rays.
The rays are initially radiated in all directions by the antenna feedpoint, then are converted by the dish curvature so they are all effectively travelling in the same direction, parallel to each other.
The wavefront does diverge over distance, so the "rays" are no longer truly parallel at the receiving end, but there are a sufficient number which are "near enough" for practical purposes.
At this point, the dish antenna intercepts some of the "rays" & focuses them back to a point at the antenna feed point.(this is the only time any "focusing" takes place)
OK, the "rays" are just a convenient way early Optical researchers invented to allow them to draw those nice diagrams in your High School Physics books, but they make visualisation easier.
Point to point microwave services usually top out at about 30miles or so.
100 miles is really stretching things.