I found a solution, for anyone running into the same issue. The ScrollingMessageFrame keeps an indexed table of visible lines, called visibleLines, where 1 (at least in my case, with insertMode 2) is the first one, and
RefreshLayout gets called every time the frame gets resized, moved, etc.
Lua Code:
hooksecurefunc(f, "RefreshLayout", function(self, ...)
if self.visibleLines[1] ~= nil then
self.visibleLines[1]:SetPoint("BOTTOMLEFT", 0, 2)
end
end)
Where f is the SMF itself. Anyway, works for now!