HTP will sustain a combustion reaction without a catalyst once ignited, but it's not clear to me if the reaction proceeds quickly and smoothly enough to be a good idea for rocket combustion chambers.
As MSalters comments above, hydrogen peroxide "will undergo potentially explosive thermal decomposition" before reaching its theoretical boiling point,...
Partial answer because
based on a simulation
doesn't address the secondary question about changes with throttling
The paper CFD SIMULATION OF A LIQUID ROCKET PROPELLANT (LH2 /LOx)
COMBUSTION CHAMBER shows a "flame front" in the sense that majority of the combustion reactions take place in a relatively small area of the combustion chamber.
From my (probably) similarily rough understanding of L*, it's a minimum size required for propellants to stay long enough in the chamber to mix properly. If the distance is shorter than that, you will experience problems with combustion instability.
As such, having a length that's too large is certainly not as bad as too short, although the engine is then ...
I'm not going to do this beautiful beast of a paper justice, so by all means, feel free to dig into it yourself. It actually looks pretty readable, although processing all the math and theory would take me about an hour per page. But luckily, the highlights are at the end:
For chugging (low frequency instability):
"4. The frequency of unstable ...
Think of it in terms of providing enough residence time for the propellants to vaporize, mix, and burn to completion. Since most of the flow is axial, the length of the chamber contributes more directly than any other dimension to the amount of time the propellants have to burn. The second most important dimension is the throat diameter which will set your ...
It's not very scientifical, but for candy fuel engines I built when I was younger, I used simple formula to compute area of the nozzle (An) from area of engine (internal diameter) (Ae):
An = Ae / K
or for radiuses:
Rn = sqrt(Re^2 / K)
or for diameters:
Dn = 2 * sqrt((De/2)^2 / K)
for candy fuels, K of around 100 worked for me.
So for example if you have ...