Thanks for that. The silicone pad sounds like it will do the job. The porch isn’t big - 2m x 11/2m and the ridge isn’t that pronounced but I’m laying tiles so need the floor as flat as poss.
In that case a floor levelling compound is your answer. It does exactly as is says. You can buy ready mixed or powdered. Like water it finds its own level and dries rockard... you may need a cold chisel to bring the ridge down a bit first if needs be but the compound will just fill in any depressions.