Sail Stackpack /Lazy Bag design

[Tranona]

With my set up the lazyjacks are set at the start of the season & need no further adjustment.

One other point about starting a zip from the boom end is that one might be standing on the cockpit seats, reaching up to catch a swinging boom, in a big swell, to get the tail of the zip & pull the first 6 inches to get it running. Just tightening the mainsheet does not stop the end of the boom swinging.
Off Barfleur one year in a big swell, my wife tightened the mainsheet, stood on the cockpit set to start zipping on our first cover, She accidentally kicked the cleat on the traveller car, releasing it. The boom swung her out over the guard rail. The back of her knee hooked on the wire but she managed to hang onto the boom with her body over the side until the next wave swung it back & threw her into the cockpit on the other side.
On the systems I have seen, one cannot just pull a cord on the zipper, without getting the zip properly started a foot or so in the first place. I had a newbie crew who went to zip up. He lost his balance whist standing on the seat & ripped the zipper clean off the zip as the boat rolled.
After that I had the zip completely changed, zipping from the mast & adding straps.

As for reef lines, I can pull mine in from the boom. But as mine have minimal friction this is not an issue when hoisting the sail. For some I can see that might be

With my boat it is exactly the opposite. Start zip from the boom end as the boom is long and the end is easily reached standing in the cockpit. Zip can be done up as far as the front of the sprayhood while still in the cockpit. The sail is very bulky because it is low aspect ratio (and new!)but zipping forward pulls it down nicely.

You really cannot be prescriptive about such details. Much depends on the individual boat. Kemps made the new sail and stackpack at the same time and we considered all the options before deciding exactly how it would be made.

 

[geem]

With my set up the lazyjacks are set at the start of the season & need no further adjustment.

One other point about starting a zip from the boom end is that one might be standing on the cockpit seats, reaching up to catch a swinging boom, in a big swell, to get the tail of the zip & pull the first 6 inches to get it running. Just tightening the mainsheet does not stop the end of the boom swinging.
Off Barfleur one year in a big swell, my wife tightened the mainsheet, stood on the cockpit set to start zipping on our first cover, She accidentally kicked the cleat on the traveller car, releasing it. The boom swung her out over the guard rail. The back of her knee hooked on the wire but she managed to hang onto the boom with her body over the side until the next wave swung it back & threw her into the cockpit on the other side.
On the systems I have seen, one cannot just pull a cord on the zipper, without getting the zip properly started a foot or so in the first place. I had a newbie crew who went to zip up. He lost his balance whist standing on the seat & ripped the zipper clean off the zip as the boat rolled.
After that I had the zip completely changed, zipping from the mast & adding straps.

As for reef lines, I can pull mine in from the boom. But as mine have minimal friction this is not an issue when hoisting the sail. For some I can see that might be

Trying to come up with a one size fits all solution for every boat wouldn't work. Clearly you like your system but it would be useless for us. I don't recognise the problems you have. A zip from the mast end would be a nightmare for us. I have never seen any stackpack that zipped from the mast first.
Lazyjacks being adjustable is an important issue for us. Once the full sail is up, we don't want the stackpack to interfere with sail shape. On a long passage we will often roll the sides of the stackpack up and tie it off to the boom to reduces chafe on the stackpack and sail. The lazyjacks hang loose and don't interfere with sail shape.
Our stackpack is tall and deep as our sails are large and heavy. We don't need straps around the sail as the stackpack contains the sail in all weather conditions, except the very strongest conditions when we have three reefs in. In this situation, we can simply zip up the stackpack over the reefed portion of the sail at the back end of the boom and control the sail. The lazyjack lines would be tensioned in this scenario as sail shape is less of and issue

 

[Stemar]

Another advantage of adjustable lazyjacks is that you can lower them out of the way when (not if) the main has a strop and insists on catching them with the battens.

You can reduce the number of times this happens by having the lazyjack line nearest the mast close enough to the mast that it guides the top batten

 

[Daydream believer]

Another advantage of adjustable lazyjacks is that you can lower them out of the way when (not if) the main has a strop and insists on catching them with the battens.

You can reduce the number of times this happens by having the lazyjack line nearest the mast close enough to the mast that it guides the top batten

One can normally set the lines up to avoid snagging. Having battens that are flush with the leech also helps. i do not have that problem. But I do hoist my mainsail by heading up to within 15 deg of windward- (to keep the boom just clear of my head & so I can see it going up)
But as said earlier. What fits one boat may not suit another. I sail SH so more adjustments than necessary are a pain. My ideas are out there for others to consider. They can ignore if they wish. From comments above, many will. But to each his own.