disclaimer: the following is simply me repeating what I've read plenty of times, not only elsewhere but also on here from Genetic Freak (I think. Sorry if I'm wrong, GF

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The ester attached to the hormone has nothing to do with the symptoms I describe, like the water retention. The differences between the esters are a number of carbon atoms, nothing more. The ester itself is responsible for nothing. HOWEVER, with longer acting esters often goes hand in hand with a less-frequent injection regimen. THIS is where the issue lies - not with the ester, but the injection frequency resulting in a more extreme sine-wave of unestered hormone levels. Injecting once a week, as opposed to every day, will result in a larger spike in blood concentrations immediately following the injection, followed by a slow decrease until the next injection. By injecting every day, this initial spike in levels is much less significant, and the decline in blood concentrations of unestered hormone will be lessened. More or less a graph showing unestered hormone levels over time will show a much more consistent level, rather than the spike and trough every week.
It's been suggested many times that this spike and trough sine wave from less frequent injection can result in an increase in side effects, such as water retention, as your hormone levels aren't consistent. I don't fully understand how or why enough to explain further, but it makes sense in my head, particularly the way it's been explained beforehand. THIS is where the anecdotal claims that Test E/Cyp cause more estogenic sides like water retention than Test Prop, as with a longer acting ester comes a less frequent injection schedule. I mean, that's the whole point of a longer acting ester, no? So by injecting every day regardless of the ester in use (in my case - nandrolone undecanoate vs nandrolone phenylpropionate), I avoid this spike and trough, and therefore avoid the increase in side effects. At least in theory.
I'm aware injecting a longer ester more frequently won't make it faster acting by any means, and the cycle length will still need to account for it. It'll still take just as long to build up, and just as long to clear out.