the order books have alot of hidden depth, so its probably not a good idea to do this kind of calculation.
I guess you could argue that there is hidden depth on both sides, so its not a honorable indicator.
a better indicator, would be to know why the walls are where they are and how they will react when filled ( will they get canceled? will they get filled and more will appear? will they move if not filled? why? )
there's no way to know all this... so we look at how the market behaves, and guess.
my guess, your calculation is 100% right.
I am assuming that exchanges do not not have hidden depth in sense that there are orders which are not visible in the orderbook.
But you are right that there is no way to tell how many resources are idling on the exchange beyond the orderbook.
I liked your idea about trying to show the walls behavior in respect to the market moves.
And I think such indicator can be constructed, for example a kind of market strength or depth relative power, which would account not only for what walls are currently in orderbooks but also how in fact of big sail/buy they really did thier stopping job.
Can you see for example if we have currently 10k bid wall at some price and in a later moment big ~10k sell occurs there are several variants what can happen in regard of this wall :
1) wall did its job and price did not actually changed significantly - wall was eaten up
2) wall was canceled right before sell order execution - then the price moved as if there were no any wall - a kind of fall from the cliff
3)...
this two cases can be measured before and after the event to calculate expected and factual resistance of the depth. To tell was it real or was it fake. A level of maturity of the illiquid market can be seen, a answer to the question to which extent market has healthy funds and not manipulators funds.
