Hi Ben and welcome to the forum!
It sounds as if your RadarBox is working OK - you are getting some flights, some of which are showing position - so it's not all bad :-)
Your lack of flights is probably down to two factors - first, many US airlines don't broadcast postition, especially domestic flights - for example, Southwest Airlines has NEVER appeared on a RadarBox screen yet - we hope that this will change over time as ADS-B becomes adopted more widely, especially in the USA.
Secondly - it's down to the position of your aerial. As Mode-S signals are strictly line-of-sight, aerial position is of huge importance, and the higher you can get it the better.
Read through some of the threads on the forum for (seemingly endless) discussion of this topic.
Hope that helps.
Rod
