Seriously consider putting a door on the front and/or back. I’ve found that a door gives better weather protection for weight than the extra fabric required to do the equivalent as just tarp.
I’ve done a lot of tarp camping this year in the UK and so have weather tested lots of designs.
A closed end is the minimum weatherproof design:
Ultralight Small Solo Tarp
Simple with doors both ends here:
Ultralight Solo Tarp/Tent
I’ve also started to use a mixture of toggles and velcro for door closures because of weight and simplicity.
I’ve not worried about caternary ridges too much – a decent bit of tension in the guy ropes is often good enough…
I’m 6ft tall and I’ve found that although a 2.5mx1.8m flat tarp will weather a storm if pitched low and in shelter it is far from a fun way to spend a night. A shaped tarp with doors weighs less and gives more weather protection.
I also must declare that I match the tarp to the weather – if good weather is expected I take a smaller and lighter tarp…