Miniaturisation removes useful volume
A smaller product leaves less room for both the battery and the antenna. Those two components strongly influence operating time and RF performance, so miniature design is fundamentally about balancing constraints rather than simply shrinking the circuit board.
The antenna is usually electrically short
At common RF frequencies a highly efficient resonant antenna may be much larger than the product can accommodate. An electrically small antenna can be matched to the transmitter, but its radiation efficiency may still be limited. Nearby batteries and metalwork can further detune it.
More RF power is not a free solution
Raising transmitter output increases current consumption and heat while shortening battery life. If the antenna is inefficient, some of the extra transmitter power is lost before it is radiated. Improving the total RF system is therefore more effective than treating output power as the only range control.
Receiver performance can recover margin
A low-noise receiver with appropriate filtering and demodulation can make better use of weak signals. This is one reason professional systems are designed as transmitter-and-receiver pairs rather than evaluated only by the miniature transmitter.
Installation changes performance
The object surrounding a miniature device can become part of the antenna environment. Conductive surfaces, wiring and enclosure materials may change impedance or radiation pattern, so representative product testing is essential.
How to interpret “long range” claims
A credible claim should specify test conditions, antenna arrangements and whether the measurement was line of sight. For miniature equipment, exceptionally large range numbers without environmental context should be treated cautiously.