Let's take 5.5 inches as your primary largest circumference size. We have to restrain the base from going any further. What you have is not a rugby shape but an invert baseball bat. This is highly common for most males in the world. The glans always tend to be the smallest.
So, our main point of attack is to get a cylinder that fits well with the base. Your base is currently 1.75 inches for the diameter of the cylinder. Everything has to catch up. That means you need to start out at 1.75 inch cylinder. This allows your mid shaft and glans to catch up. Once you pump the first or second set, you'll notice the mid shaft if will tighter, but there are plenty of room for your glans to continue to expand. If you cannot get your penis into the 1.75 inch cylinder any more because the base and mid shaft becomes too big, go to the 2 inch cylinder now. This allows your base and your mid shaft to continue to expand.
The trick going up with constrictive sizing is to also help with your erection quality. How so? By providing your penis time to hold onto the rigidity of the penile base tissues all the way up to the mid shaft tissues. You're not forcing all the tissues to work at the same time. Just the upper shaft tissues to expand laterally. Your routines work on the LengthMaster will force your longitudinal growth for length, but that won't cause fatigues for the base to mid shaft. This allows your penis to build up stronger rigidity to help out with your ED.
As your penis becomes more uniformed, you'll notice your erection quality becomes stronger because you have more equalized blood flow, rather than abnormal blood flow. What do I mean by that? You currently have a lot of blood flow at the bottom to roughly the mid of the shaft. But there's a bottleneck, or reduction, of flow to the glans. There's not enough blood volume to push through the glans for stronger rigidity because the blood vessels are not supporting larger transport of blood volume to the upper part of the shaft comparing to the bottom. That may be the reason why you're reporting in only 70% to 80% rigidity (erection).