The various cans on the market are not the same internally.
Your short header setup -which you noted worked well , may not work well on a Vtech setup.
big internal differences:
First is the overall length of the header tube-which extends into the can.
Next, the distance from the end of the "header", to the reflector.
Then, the PRESSURE in the expansion section.
This is never addressed in any of the so called text books on pipes I have thumbed thru - rather, they dwell on theoretical wave forms etc..
In hands on testing , we found that changing the final exhaust outlet size, could make big differences in the engine response.
One test setup I made, had a trombone setup for the header tube in the can.
The can moved fore/aft as the header remained constant in length.
The result being that the can volume remained constant ,yet the reflector distance to the header outlet varied.
also---- the final outlet flow to atmosphere, from the contraption , could be regulated.
A pressure gauge,tapped at centre of the can body, showed internal pressure.
Power boost was ALWAYS accompanied with a rise in gauge pressure.
I have a goofy tuned setup , for my 50 -which is simply a header 6" long dumping into the lid end of a pint paint can and the exit being a small dia exit tube running into the bottom end of the can.
this setup does tune -but is very peaky.
It also requires the engine be set "four stroke" rich on the ground.
I get inquires as to proper length for headers -
unless I know the entire setup - engine/can/prop/desired performance - I really don't know - but try to answer on the conservative side.
The Pefas are different cats -compared with KS and KS also has differences in performance in same sizes -such as front in /out and front in /rear out.
The Vtechs are another approach and I found that the smallest setups which really work -are permutations of that setup
They also have a noiser note in the air.
All of these differences in cans/ operating lengths and the power band being addressed , obiously cause confusion.
I get the std question," I don't give a shet why it works, I just want the best setup" and that answer is simply an unknown.
At least ,for me.