Corey:
I'm facing the same dilemma as you are concerning risk control. With summer around the corner and the expectation of low volume choppy days, I figured this might be a viable strategy so I have been working on this strategy with one pair that appears to trade somewhat consistently with each other. My conclusions/questions are the same as yours (sorry I don't have any answers for you).
On choppy days, this strategy seems to work very well but on trending days it seems that I could lose a weeks worth of profit in one day by averaging into a spread that is going against me. I feel like I'm trading off of stochastic bands i.e.: telling the stock what it SHOULD be doing, and basically fighting the trend. What's more is that when a sector starts to trend (either up or down) I am always buying the "weaker" stock and shorting the "stronger" stock, which is completely counter-intuitive to me. If a sector starts to move up, I want to be long the strongest stock and then I look for the weakest stock so that if the sector turns around I know which one to short.
As you pointed out, the key probably lies in the subjective view of the trader (as with all strategies of trading) and a pure mechanical approach based on fixed parameters would be doomed to failure (especially for me as I do not want to have any positions overnight, and therefore must exit by the end of the day). What I have noticed though is that if I approach it as a one sided trade first, and base everything on tape reading I can be profitable by taking some quick scalps when the spread widens a little too much on one stock.
Right now, my entries are based on two different setups (still looking for more) with the condition that the spread is approaching a short-term extreme level (I do not use a "set" value to determine when that is, as I'd rather go by "feel"). The first is when one of the stocks gaps up/down (in the appropriate direction) or has an unusually wide spread that I can take advantage of. If I can get executed, I look to exit that position with a quick 10-20 cent scalp. If it looks like it's going to take a few minutes I then focus on the other stock to make sure I can still hedge myself. If the original position turns sour I first try to get out of that position. If I can't without giving up too much, I'll take the second trade on the other stock.
The second setup is when I have a large bid/offer to lean on in my favor on one of the stocks. If I'm looking to buy stock A and short stock B, and stock A has 20,000 for sale on a tight spread, I will short stock B and look to make a profit on just that leg, unless I'm forced to take the other side if others start taking the offer.
My exits are solely based on the tape right now as far as taking a loss is concerned. If I'm losing on the spread, I try to evaluate the trade in terms of the present situation. If I'm long stock A and the tape looks weak, I will exit immediately and look to re-enter at a better price. The same is true on the other side of the spread. The problem arises when the tape really doesn't tell you anything, but the two stocks keep drifting slowly in the wrong direction. In that case I will only average down in the spread once, and keep an ultimate tight stop about 5 cents away. But to be honest, it seems like whenever that scenario happens, I tend to get stopped out, so I'm really not confident that that is the best solution.
So far these two methods have been somewhat profitable for me whereas just selecting values to enter the spread has not. Unfortunately it requires much more attention and energy on my part and I wonder what the opportunity costs are as it's hard to keep track of other potential trades. I also wonder if I have put myself at a disadvantage by trying this strategy on a pure intraday basis as opposed to a longer-term basis.
Hopefully others will shed some light on this based on their own experiences.
Darren