Micro box ranges with suppiled antenna

[acars45]

What was very strange today as you know i took my dongle to biggin with the supplied antenna to being with i was getting really good distances    Over 200 miles then suddenly dropped to under 100 miles I'm no expert  but I'm no expert so I apologise what causes the big difference is mileage is it high pressure systems wind speed direction any help if anyone knows would be fab look forward to your repiles

[acars45]

For example i was at biggin hill airfield 600 feet above sea level  i was getti g excess over 200 miles from the suppiled antenna and i was getting a lot of traffic in wales right up to
Haverfordwest which is a good distance
Then suddenly the tange fell by half
Any ideas