I am a little confused about density

I have understood so far that density of 0.30 equals 1 stop. (same as saying 0.10 is 1/3 stop) . so if this is true for all fims (not sure), why is it that in my results (shown below) the numbers do not move in 0.30 increments for each zone. ?? They seem to be moving up in around approx ~0.15 (give or take) density increments, instead of 1 stop = 1 zone increment = 0.30 density. Why is that ??

Notes: the Film was Tri-X 400 35mm format. Developer D76 1:1 process as close as possible to Kodak recommended settings. That is, agitation pattern, time, etc.
I shot this test roll under sunny day in open shadow, light did not change as there were no clouds early in the afternoon, and camera meter matched the F16 rule... which gave me confidence that I was exposing somewhat correctly.

Now, With small 21-stp stepwedge measured in exact same way, 1 stop increments does in fact match very closely to 0.30 increments in density... (I didn't post this results as it is not needed, assume true)
This throws me off because I was assuming that to raise zone VIII to IX, I had to increase the density by 0.30 , but the numbers (column N) in my film as well as in Appendix 2 of AA box do not correlate to this. In fact. if recommended density for zone I is 0.10 and for zone V is 0.65-0.70 , there is only 0.55 of density between them. I was thinking each zone above zone I , I would have to add 0.30 that would add up to way past 0.65 recommended for zone V. Can someone clarify this for me. ? (by the way for this test column N-1 is -30% less time, and column N+1 is +30% more time).

 Zone N-1 N N+1 1 0.02 0.04 0.05 2 0.08 0.14 0.17 3 0.19 0.31 0.40 4 0.32 0.53 0.63 5 0.46 0.71 0.86 6 0.58 0.88 1.09 7 0.69 1.00 1.20 8 0.83 1.19 1.41 9 0.99 1.37 1.61 10 1.12 1.54 1.80

Thanks,