Moderator block tooltip indicates that it should only activate when adjacent to a reactor cell, however it seems to have a significant effect on reactor output when placed between to active moderator blocks. Not sure if this is a tooltip issue or a defect in the algorithm.

I'm using 2.9e on 1.12.2 (FTB Revelation Pack v1.8).

https://imgur.com/a/HngOl

The reason that you're getting the boost is because the extra graphite is completing the moderator line between the two cells. You can now have up to four moderators between cells for an efficiency boost :)

oooh this means that I can go back to some more designs.... hrm....

Hrm I notice that only the moderator touching the cell is "active", so far as cooling blocks are concerned. You can have four moderator blocks between cells, but only two are "active." This is confusing =/

Yeh, it is not obvious at first, but some designs really do benefit from having a very spindly cell structure :)