In fact, I think I am on the upper range because I didn't sparge correctly. What I did was I took my pot where I mashed for an hour, then I drained the syrup from the pot to the boiling kettle. I then filled up the 'mash' pot where the grainbed was with sparge water (at 75C) and then left it there and drained it after 10 minutes. SO, I'm thinking I lautering too fast hence resulting in a higher pH. I think I saw this relationship between lautering rate and higher pH values in Palmer's book somewhere. Now, I did another batch with a proper insulated mash tun. And did the sparging by the book, i.e. slowing draining wort from the drain at the bottom of mash tun and adding a litre of sparge water, for every litre of wort I got, at the top of the mash tun.. so to keep story short, I nailed a post-boil pH of 5.2 head on! So maybe all this is because of sparging incorrectly.. hmm.. what do you think?