Not sure of the actually LOP of the A2, somewhere around 13.5", but the A1 is apparently 5/8" shorter. There's always the Sully Stock with an 8" LOP or the RRA or Bushmaster Entry Stock at 7.25". I'd personally follow the recommendation of the collapsable stock though...lots of options and flexibility and I wouldn't even hesitate to throw one on a 20" rifle.
Here's an older review I had on file of a few different collapsables and their LOP's (some of the info is now obsolete)
5) Adjustability - How many positions does it have? Can it be easily opened to your preferred LOP
MagPul M93A - This stock offers more positions (8) than any other stock on the market. It is also the only stock that allows the user to set-up LOP presets. Fully collapsed, it's about .25" longer than the M-4 closed (10.04" LOP). When fully extended, it's about .5 longer than an A2 stock (13.98" LOP). Clearly, the M93A offers more adjustability than any of the other 3 stocks.
Ace M4 SOCOM - This stock has 5 positions in 1/2" increments and it comes with either a 1.0" or 0.5" recoil pad. There are no preset options. There are 2 versions of thi stock available. The shorter version has a length of pull (without a recoil pad) that can be adjusted from 11.0" to 13.0". The longer version has a length of pull (without a recoil pad) that can be adjusted from 13.0" to 15.0".
Also, for folks in states that still have an AWB, you can swap out the push-button with a supplied set-screw to "fix" the stock at the user specified length.
LMT SOPMOD - This requires a mil-spec buffer tube which are available in either 4 or 5 position versions. If you use a 4 position buffer tube, the minimum LOP will be 11" and the maximum LOP will be 14.25" which makes the LMT SOPMOD stock the longest one out of the box.
Vltor - This requires a mil-spec buffer tube which are available in either 4 or 5 position versions. The buffer tube offered by Vltor as 5 positions. Minimum LOP is 10" and maximum LOP is 13.32". There are rubber butt pads available for this stock if you want to increase the LOP.
Standard M-4 - These do not require mil-spec buffer tubes with the exception of genuine Colt stocks. Buffer tubes are available with 4, 5 or 6 positions and I believe there is even a 7 position one now. Minimum LOP is 9.84" and maximum LOP (with a 4 position buffer tube) is 13.18". If you use a 5 position buffer tube, the max LOP will be right around 13.32" If you use a 6 position buffer tube, the max LOP will be around 14". There are also rubber butt pads available for this stock if you want to increase the LOP.
Hope that helps!