I know what you're thinking, but you're only thinking about YOUR setup. It's one of those "square is a rectangle, but not all rectangles are squares" scenario. I'll try to explain my best!
This depends on how the system is setup and how the bypass is "tee'd" off. There are times where the benefits of having the valve on the same arm as the reactor ISN'T of benefit.
Example 1a:

Flow is correct, despite valve on opposite arm from reactor
View attachment 16177
Example 1b:

Flow primarily skips arm with valve, majority of flow isn't controlled (despite valve being on reactor side).
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Example 2a:

Flow is correct, with valve on same arm from reactor:
View attachment 16179
Example 2b:

Flow primarily skips arm with valve, majority of flow isn't controlled.
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This property applies to setups where it has two return lily pipes, too:
Example 3a:

Flow through system is properly controlled with valve on reactor side
View attachment 16182
Example 3b:

Flow primarily skips arm with valve, majority of flow isn't controlled.
View attachment 16183
Switch where the reactor is relative to the "Tee":
Example 4c:

Flow is correct, despite valve on opposite arm from reactor.
View attachment 16184
Example 4d:

Flow primarily skips arm with valve, majority of flow isn't controlled.
View attachment 16185
Example 5a:

Niche case, where there is no "main" path of flow because the Tee fitting splits the flow equally. Technically you have same amount of control whether the valve is on the reactor arm or not:
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You'd have the same control/flow because of the evenly split tee, but the overall AMOUNT of control/flow you have is far less than if you just...
...6a:
View attachment 16189
6b:
View attachment 16188
Or, if you swap the arms where the reactor is:
7a:
View attachment 16191
7b:
View attachment 16190
The summary here is:
Water doesn't like to turn corners, ever, unless it's either forced to by gravity or because it has nowhere else to go. Water will ALWAYS choose the path of least resistance, so we want our valve to be placed in the path of least resistance, not the path of most resistance. This is an important basic for fluid dynamics.
In SOME cases that is a true statement, but there are other cases where that is false. It's not a blanket true statement that what matters is that the valve is "always on the arm of the reactor". Sometimes it is supposed to be on the opposite side. It depends on how your tee is oriented, and which arm contains the "main" flow, aka the path of least resistance, for the water.
Hopefully these examples help show the most important truth: What is most important to control the flow through your reactor is to
always have the valve on the "main" arm, the one where the water has the path of least resistance. Sometimes that's on the reactor side, sometimes that's on the bypass side, but it should always go on the reactor side for full control.
I hope this makes sense! Your reactor is set up properly, because it technically looks like this:
View attachment 16194