The splitter was done before the first box. Whatever plan you have, your dish will supply it to your boxes 1, 2 and 3, individually and independently.
Please note, it is the other way around.
The box supply the DC power to the LNB for you to receive the signal.
the LNB is rated 13-15VDC
that is the reason why on basic residential set-up. only 1 STB should be in LNB powering.
why? do the math... all STB in LNB powering would mean 13V/18V coming from each STB going to the same LNB.
we used to install DC block on secondary units to make sure no power will be provided to main box even when you do a factory reset. it is now mitigated by software switch function that is LNB powering.
Also, the satellite splitter being used is a power divider "ALL PORTS POWER PASSING"
that means, it lets any power coming into the "OUT" ports to the only "IN" port.
So, it is possible and very likely that boxes with LNB Powering ON on all STB setup are viewing them not at the same time.
For me, I will stick with the Main ON, secondary OFF setup. All ON setup may damage your 1. Splitter , 2. LNB or 3. STB (should be ok, if under warranty
btw, this is my personal opinion as subscriber and does not reflect CignalTV as service provider. thanks