the Sirius was made in a Standard and a Large. our paddling group has a number of Tsunamis and I found that the Large will fit the 145/125 and also the 140/120. The Standard only fits the 135 well.
I'm thinking you may be happier with a neo deck skirt, the neoprene has much better stretch/give than a nylon skirt. Snapdragon makes some skirts with a breathable tunnel and they make 50" and 55" tunnels for big guys. Expensive but a good investment.
maybe (and pls. don’t take it as a slam) you need to practice putting on the 1.7 skirt. It isn’t an intuitive thing, there is a certain sequence that works.
your profile says you are in PA. You might like a neo deck bec. it will keep you warmer in spring and fall.
It also repels water and waves without pooling like nylon skirts can. As said above, neoprene is stretchier and conforms better to the coaming. It will do so even more readily if you wet it first.
If you have any interest in eventually learning to roll the neo skirts take on way less water. Or if not, you can carve deeper edges w. a neo skirt without water coming in.
Pricier yes but last longer and more performance.
Both Seals and Snapdragon offer specific sizing in their neoprene tunnels (XS thru XXL) and can further customize for you. Love my Snappers. Both are excellent companies - they will have a skirt that works for you.