I’ve already decided to get a Harris, with the notched legs (as opposed to tension screw) and I’ll be getting the S series (rotate 45° for instant leveling on uneven ground).  

I had originally thought the taller 9”-13” bipod would be best but when I lay down (prone) and hold my rifle it just doesn't seem to be up that high.  I’m interested in comments from people who have used either height bipod and suggestions on which is better for bench-rest or prone positions.  

Any comments are welcome and appreciated.  Thanks!

I use the Harris S-LM 9-13" with bipod spikes with the S-lock. It is amazing to use. I would suggest a vortex scope bubble if you shoot on uneven terrain. This bipod rides on my LR308 and works awesome.

You also have to take into consideration the magazine.  Too short and the mag may contact the ground or be difficult to swap out without raising the butt of the rifle.  Some would say you can always put something under the bipod to raise it up, but then that is one more thing to mess with and not always practical.  I prefer the taller version.

I've been using a 9-13" for a while and just recently switched to a 6-9".

Generally speaking I think the 6-9" is more versatile. 9-13 is too high for prone on pavement/short grass/dirt etc. I shoot from prone in an area with a bit taller grass and the 9-13 on its lowest setting when prone is pretty much perfect, but I rarely would need it any higher than the lowest setting.

The notched 6-9 is actually slightly longer on the longest setting than my thumb screw 9-13 on the shortest, so it works well where I shoot.

Another good point I've heard and tend to agree with from experience is that if you find the bipod too short in a certain scenario you can typically find something to put under it to make it higher, like a pack or log, etc. The same is not true when you have a bipod that's too long and you need it shorter. Definitely something to keep in mind.

6-9" is perfect on my large-frame AR for prone shooting. 9-13" is too high for comfortable prone shooting, and usually not high enough to get over vegetation or terrain. In that case, it's time to bust out the tripod.