Tail rocker does not change angle of the board at all.
There is quite some space after the mast, where your foot is placed, and sometimes a tad more (there should be, so you can stand wider and ride waves t.ex).
A foot from center of mast to board end, sometimes more even on supershort boards.
Having rocker here behind the mast wont change the board angle at all.
Pretty sure this is what slowboat asks about, and not the board angle nor nose rocker or center rockerline.
Having tailrocker (actually tailkick as we use on surfboards) will give a much smoother transition when waterstarting, up to foiling, especially if choppy, and touchdowns and back up in chop or waves or flat, will feel a lot gentler.
Opposite, a flat tail will start earlier, no matter what.
Another parameter that will give you the same effects, is whether you have a wide or a tapered (narrower) tail.
The tapered one will be smoother up/down when starting or in touchdowns, and another advantage is you can carve REALLY hard turns, without catching with the rear edge of the board, really good thing IMO.
The downside is, same as with tailkick, that they dont start as early if underpowered.
Horses for courses.
IMO it is somewhat like waveboards, a few mm here and there, and the overall context of all small details, can really be felt hugely and not possible to know beforehand - it is the full constellation and how it FEELS, it is all about.
Only difference is, that on a waveboard you use it all the time in the water, so critical, on a hydrofoil it is for starting and touchdowns only - but this is often a major part of hydrofoiling too
Individual likings - but it means A LOT, thats for sure