@MySong, in your original post did you mean that your main sheet was eased until the SAIL was against the spreader bar or until the BOOM was against the shroud?
Even if you don't intend to ever sail with your boom all the way out to the shroud, due to sail chafe concerns, I don't think it's a good idea to make your sheet so short that you CAN'T let the boom out to the shroud, for example when heaving to or just trying to completely unpower the main in an urgent situation.
If you want to make sure the boom doesn't actually hit the shroud, you could certainly put a stopper knot in the sheet at the appropriate spot, and leave some additional tail after the stopper knot so you still have something to pull on if the stopper knot ever does get all the way to the cleat.
Regarding the designed use of the H26 main sheet for mast raising/lowering, the owner's manual specifies that the main sheet is 70' long. I haven't measured my main sheet, and I haven't taken note of just how much main sheet I have left when my boom is out, but one other thing you could check is to see if your sheet is around 70'. I also can't remember how much main sheet I have left when rigged for mast raising with the mast all the way down, so I don't know what the actual required minimum length is (vs. the factory spec).