Yes last 6 is actually 2.167. So on that (rather last 8 as Simster noted the 1.625 comes from) we'd finish on 81.839 which looks to be more like 3rd place.
My mistake 1.625 ppg is based on last 8, you are completely correct to say last 6 is 2.167 ppg in other words 81.84 points or 3rd.
Still think another 29 points (1.71 ppg) will almost guarantee a play off spot: Any of these will do and based on the revised ppg over the last 6 it's achievable:
a) W6, D11, L0 = 29 points
b) W7, D8, L2 = 29 points.
c) W8, D5, L4 = 29 points.
d) W9, D2, L6 = 29 points.
e) W10, D0, L7 = 30 points.
Check my maths first!