Cock Variance: Custom Cage Sizing Compared to the CB6000S

What’s the best way to measure up for a custom piece? I understand that you’re supposed to take measurements when everything is at its smallest (not shriveled), but every time I look down, I’m unsure what counts as the true minimum. Is it while standing? Or while sitting? My relaxed state seems to shift by about an inch. I want a device that fits my absolute tightest possible size, which would feel nearly snug even when seated. But will such a fit be too constricting for sleeping? With my CB6000S, it’s usually pretty full when I’m standing up, though there’s sometimes 1/4” to 1/3” of wiggle room (using the smallest spacer). When sitting, that gap grows to between 1/4” and 1/2”. So, if I order a custom unit (likely from Steelworxx), should I play it safe by going 1/4” smaller or go all out with one that’s 1/2” shorter? Another concern: when the device is pressed firmly against my body, the CB6KS fills up completely, but normally sits a bit loose. I’m leaning towards getting a slightly tighter ring if the anatomical part feels right. However, if the device hugs closer to me, I worry that ordering anything other than an exact match for the CB6000S might end up being too small… The dilemma continues! Any advice before I spend the money would be great! Thankfully Steelworxx isn’t currently taking orders!