I was bored, so I did some more testing.
It appears that FoV range is dependent on the attack speed.
Potential Explanation:
Since FoV attack is *slowed, the hitboxes of the attack are delayed. This is important because the hitboxes are delayed towards the end of the forward movement, instead of the case of Caliburs and Brandishes which have their hitboxes activate towards the beginning of the forward movement (thus having less range). FoV doesn't have any more range, it's just that the range seems farther because of the delayed hitboxes.
Thus, ASI affects the range of FoV regular (and also Brandishes and Caliburs), but this is to quite the minor extent...
The 3rd strike of the ASI+6 FoV has roughly half block less of range than the 3rd strike of ASI-2 FoV. (my test target doesn't hug the obstacle perfectly, and I have to line up half-blocks by eye)
For the hell of it, I also did the test with my LHB. And surprisingly it's also like half a block. So if you notice you often whiff your 3rd strike of the combo, it's probably cuz you got high on ASI. Because that half-block matters more for the Calibur than the FoV.
tl;dr ASI and MSI the everything, cuz range don't matter none.
*EDITED: "delayed" to "slowed" for clarification.
Sorry, took a hiatus, what is the LHB?
Also, I agree with your results. Having a no ASI FOV made the 3rd hit much more consistent on hitting than the 3rd hit when I used a SSB. I used to test this with skellies in FSC when I went FOV only runs. Third hit would randomly miss. The charge though....beastly
So you are saying that, if the FOV has over a certain amount of ASI, the third delayed hit gets cancelled due to the speed resetting the attack sequence too early in combination with the delayed attack? Maybe delaying the hit was a cheap way of decreasing the attack speed slightly.
Nevertheless, it is a bug, and won't be fixed. As usual.