Why is this happening ... according to websites that can be trusted, the answers are different -

https://mathworld.wolfram.com/CirclePacking.html

http://hydra.nat.uni-magdeburg.de/packing/cci/

In other words, these are not the optimal values,
i.e. for test 8
the value using the simpler (and not accurate formula) - 3.6131259 is accepted,
when the optimal value is less than that - 3.3047648