Comparisin of Similar Tracking Sites


I am somewhat puzzled to find that comparing Flight Aware and another Airport Tracker when monitoring Heathrow traffic. I find that Flightaware displays 14 aircraft and the other package 42. I have tried various attempts to improve the number of displays to a more realistic comparison. Who is correct and why??

Having ventured further I now realize that by having both tracking sites in their own respective pages by slightly reducing the size of the display page for FlightawareI can lose half the aircraft displayed. Is this correct?