Uh, I hate to hijack this thread back to the original question but...
Will a set-up in an irregular sized room work or do the walls need to be equally spaced to do the the job. Can the output to one side be increased to make up for the open space? And - is my Yamaha RX-V2500 up to the task?
In order to reproduce equal acoustic output from each driver, symmetry is always preferred...that includes not only dimensional symmetry but also acoustic symmetry. The material that the speaker sees as the first reflection should be the same on both sides or walls - and usually we want to create some absorption at that first reflection anyway. However when those times arise where you cannot accommodate symmetry, there is not much you can do to get the reproduction like you could if the room was symmetrical to begin with.
Sure you can increase the output from one speaker to accommodate the loss or greater distance from one wall over another, but it is not going to obtain the same results. In fact you will most likely distort the balance and imaging. In a non-symmetrical setup, you will be missing the interaction of the wall near the speaker. This will cause anomalies such as, uneven acoustic reflection, comb filtering or cancellation due to resonance, whether it be constructive or destructive interference and more.
Sometimes if you are far off of one wall with respect to the other channel(s), it may be best to install some sort of large (moveable) panel which duplicates the surface of the other side. If possible set your speaker which is closer to the inner corner of the room where you say the television is located. In other words don't push it out so far into the open area which makes up the inner "L" of the room.
If you have no choice but to locate the speaker out in the open area where the "L" is, then you may want to provide some absorption to the speaker which is on the opposite side of the room to the one closer against the long wall. The reason I say this is because the speaker out in the "L" (short wall) will not have as much reflection. I would not recommend increasing the level or changing the balance more to one channel over the other.
As far as your receiver, I don't know much about the Yamaha to comment on that. Impedance of Electrostatics can dip very low at certain frequencies and only the robustness of the Yamaha internals (hefty power supply, high current output stage, sufficient reserve and capacitance) will tell if it will do the job or not - particularly at higher volume levels.