There are many different algorithms of analysing flight performance, and they all have small and subtle differences in what they regard as thermalling, cruising, turning and the likes.

I'm currently working on developing https://skyhop.org as a way to analyse flight performance without having to hassle with IGC files, and I bet it'll show a different value again given I'm using a value calculated by an XCSoar derivative. Only limitation right now is that you would need Flarm in your glider (and again, this collection method would also skew data a bit).

Ps, I'm just starting out on this endeavour, so if anyone has feedback on the tool, I'd love to hear about it!