Order in the madness ... 
Hey Scott, It sounds like you are doing things in the right order. Your description "... I normally attach the tack to the hook and then tension the halyard before tensioning the clews reef line. I have to go forward to attach the tack, then I normally go back to the cockpit to tension the halyard and then tension the reefing line which is led from the gooseneck down to a fairlead at the base of the mast and back through a deck organiser and then a clutch to a cabin top winch." Is a perfect example of why I'm not a big fan of leading main halyards and reef lines aft. What holds the the sail on the reef hook while you go back to tension the halyard? Too much walking back and forth for this old man.
Peter gets away with, "When reefing, I ease the mainsheet and vang, tension the topping lift, then drop the sail until I can hook the tack cringle over the ram's horn, including the sail stop juggle. Next, I tension the reefing line, which on my boat only controls the clew of the sail. With the halyard slack, the sail is so loose that the reefing line (it should be rigged to pull the clew down and aft as PaulK and Vern mentioned) tensions the new "foot" of the sail properly. Then I rehoist the sail, tension the halyard, ease the topping lift, sheet in and I'm gone." The usual order is to ease the halyard, secure the tack, and re-hoist ... then tension the reef line. On many boats if the reef line is tensioned before the halyard the sail can be damaged. If you know (as Peter does) that on your boat, setting the reef line first will give the proper shape you can do it in that order. One of Peter's actions is very important. He sets the topping lift! It is always easier to haul the sail down to the boom than hoist the boom to the sail. This is a good reason for adding a boomkicker or other "rigid" boom vang. Supporting the boom while reefing is a key factor. As far as the webbing straps lead through the reef tack cringles, they can add to the problem in many cases, they require greater setback on the reef cringles. When the sail is at full hoist, the distance from the sail track to the tack horn on the boom is the setback measurement for the tack. When the sail is set and the outhaul tight, the tack cringle keeps the outhaul from pulling the luff rope or sail slides out of the luff groove. Compare the location of the tack horn to the position of the reef hooks. On most boats, the reef hooks are farther aft than the tack horn. That means that the reef tack cringle must also be farther aft. If the reef tack cringle has a web strap through it and the ring goes over the reef hook, the reef tack cringle must be even farther aft. A simple test for reef tack cringle setback is to look at the sail slide just above the reef tack. If it is pulled aft by the reef line, the tack cringle is not far enough aft. When the reef line is tensioned the sail slides (or luff rope) must be free to slide in the luff grove. Another check is to ease the halyard, set the tack, tension the reef line then see where the wrinkles are as you rehoist the sail. If there is a wrinkle between the reef clew and one or more sail slides, the tack is wrong. Even good sailmakers get it wrong. I've lost count of the number of sails that I've seen than have had issues with getting good reefed shape. As a rigger, it should not be my job to "make the reefing lines work right" when all that's needed is moving a cringle ... grrrr
The damn hardware was on the boom when the sailmaker measured, why should I have to move it to fit the sail? It's like buying an Armani Suit and having the tailor send you to a surgeon to make your arms fit the sleeves.
