The wiki for chapter 18 shows a speed going from 500 to 525, or a 5% increase, when it really should have been at least matched the tech tree increase, which was about 17%, or 585. This chapter has a few less tech, so the increase is just over 15%, and that speed increase you are showing is just over 25%.
I looked and I did not see any speed boosting AW that should show up, so my first thoughts are that the wiki is incorrect, that the speed number is 550 for level 40.
But looking to earlier chapters, there wasn't enough of an increase going to level 39. It gave an 11% increase for the chapter but the tech increase was more like 13%, so level 39 should be corrected to 510, and then 17% for chapter 18, means that it should be 600, not 550, or the 525 on the wiki, and then 15% for chapter 19 is 690, so it gets to about where it should be from the tech tree, but it should be more balanced getting there:
Level 39 - 510 speed
Level 40 - 600 speed
Level 41 - 690 speed.
But that also isn't giving anything for the increase from expansions.