I've noticed the same thing... also shrouds around the futtock has this visible stretch... I guess to have enough space for the feet and futtock shrouds.
So futtock is adjusting distance between shrouds... and they are not so compressed under the top... it's quite few of them over there
I would go still with ratlines parallel to waterline... with slight angle
but more or less futtocks parallel to the tops.
Even with main channel angled you should be good with ratline tight to the first shroud on upper seizing and last one just right above lanyard deadeye.
I guess it will still create little angle... but should be all right
On top of that... top shrouds ratlines are parallel to waterline... so you will have all of them more or less same way... and not lower angled to channels upper parallel to waterline...
...by the way... I see you have ratlines stencil for whole shrouds... I did ratlines bit different.
I positioned 1st ratline way I wanted... then I just use piece of plastic card (strip) for distance jig between ratlines
I did second ratline... measure and adjust distance using this plastic jig... and then 3rd, 4th... etc...
Piece of cardboard stencil covering all shrouds from the back for me doesn't work because it's obstructing my movements with tweezers.
...it's just my way...
Cheers,
Matt