Strange - having driven '9520 for a number of years and being familiar with '9513 and '9502 these comments puzzle me. Perhaps it is a 'size of the driver' thing ? Being only 5' 8" maybe I just fit the cockpit better, but having seen taller drivers comfortable in their Mk. IV variants that doesn't seem the likely explanation. Later variants e.g. The Classic Mk. II have the same central shoulder strap arrangement and so far as I know have not been found uncomfortable with regard to neck/shoulder strap clearance.
If you ever have to live with a Mk IV variant, or later model, which has four or five point harness fitted, you will appreciate what a clever solution A.C. designed to fit a three point harness with inertia reel and, as a bonus, there is always amusement to be had watching drivers and passengers searching for a non existent strap over their outboard shoulder.....
I wonder if the driver's seat in '9505 has been moved inboard to give more space between seat and door ? I also wonder if you have received the same complaint from your passengers ?
Turning to your dread of rain: Why erect the hood ? Even in a downpour open cars keep dry so long as one keeps moving. Below 30 m.p.h. you will get rained on a bit, but then a Mk. IV (or any open A.C. for that matter) is not intended to be driven at low speeds. Moreover neither car nor driver will melt in a bit of rain.
I hope the forgoing doesn't sound critical - there is obviously a difficulty. I wonder if a picture would be worth a thousand words - could you post a 'strapped in' cockpit selfie ?
Barrie