Am limited to 9 gal total water. Currently put 5 in mash and 4 in sparge. Equipment and boil off loses gives 5.5 gal to ferment and 5 gal to bottle. Maybe it would be better to max out the water in the mash and use the rest for sparge, keeping total at 9 gal. May have to add DME to hit SG.
I think the 9 gallon water limit is the key because you are bumping into the maximum gravity that you can get from your first runnings. I have rarely seen my first runnings exceed a gravity of 1.080. Even with huge grain bills, the gravity drops off from that starting number and if you have 9 gallons in your kettle at 1.060, that will boil down to 5.5 gallons at 1.098. There is still a lot of sugar available in the mash, it is just getting thrown away.
One way to increase your water limit would be to bring 3 gallons up to a boil during the mash and put it in a corny keg. It would then cool down to sparging temp by the time you need it and you could use a cobra tap and CO2 to push it into the mash tun.
Since your boil kettle is maxed out, you could collect those runnings in a bucket. Those runnings could be added to the kettle slowly during the boil. Using this method, if you can collect 12 gallons at an average of 1.055, that will boil down to 5.5 gallons at 1.120. I think you'll find that an extended boil works really well with big beers.