This should replace the need to hook SetPoint, though you may still need the combat check.
Lua Code:
Boss1TargetFrame:ClearAllPoints()
Boss1TargetFrame:SetPoint("TOP", Minimap, "BOTTOM", 0, -70)
hooksecurefunc("UIParentManageFramePositions", function()
Boss1TargetFrame:ClearAllPoints()
Boss1TargetFrame:SetPoint("TOP", Minimap, "BOTTOM", 0, -70)
end)