Tps, starts and goals are usually represented by circles when we set tasks. This is usually fine, but when a large radius is used, errors can occur. This is because some instruments use different ways to calculate distance. For example, airspace in a 6030 is always represented as straight lines with a circle being represented as 20? segments. At some point FS was changed to include an error factor for radii to make sure pilots didn't miss out on TPs etc. (I personally disagree with this, the instrument manufacturers should fix their software so that they calculate distance correctly)
Since I recently installed SeeYou Navigator on a phone, I decided to test how it performs with big Radii, and also compare how FS and AirScore interpret the tracklog. The flight took place at Bells Beach, launching from Winkipop and landing at Anglesea. A 400m radius start from Jarosite launch was used, with a 65km radius Tp from Mariners and a 64km radius goal from Mariners. When Seeyou indicated that I had the 65 + 64km radii I imediately turned back to identify the location in the tracklog.
Visual results
I have used FS to score competitions extensively and have high confidence in its results. Here's the visual from FS with a couple of manual markers added to show times (obtained from FS by hovering over the indicated point). The solid red and blue lines are the radii, while the dashed lines are the radii plus/minus the error factor. You can see the turns I completed immediately after seeYou indicated I had the TP/goal. While 1 test is not conclusive, it appears that seeYou can be relied on to correctly indicate when you getting TPs etc. 
AirScore gives a visual of a flight using resources provided by other organisations such as Google Maps. Unfortunately, their way of measuring distance seems to vary slightly from what our scoring software uses - so if its a big circle (>20km) and you really need a high level of certainty, I would advise re-scoring in FS and looking at the FS map. The visual provided by AirScore has the radii slightly different to what FS shows. 
Scored results
Looking at the times recorded by FS and AirScore we see a minor difference for the start, but a significant difference of 18 seconds for the goal. But if you look at the visual provided by FS, you will notice the time provied by Airscore is exactly what you would expect, while the time provided by FS matches the time crossing the circle for the (radius + error factor). I would be happy to accept the result provided by either FS or AirScore. 
Note: when I first checked the tracklog in AirScore I could only see the driving that happened after the flight. Since the flight had taken place on the 04/11 UTC time, I added 2 hours to times. The tracklog still didn't load properly so I removed the section after landing... You may notice the 2 hour difference in goal times that this caused.