I guess I'm too used to the Lumagen, because I don't have a problem with low level gamma causing crushing. On this occasion I'm going to disagree with Mark as don't find that a measured 2.2 crushes black at the low end as I can see the 17 bar flashing on the AVS disc whereas if it were crushed I wouldn't be able (16 is as dark as 15, 14, etc, so black level can't go any lower).I find that a gamma of perhaps 2.3 that drops to 2.2 at 10% looks good to me (when I had a temporary black room treatment up anyway). If you slightly raise up the 5% in custom gamma it may well help without raising the absolute black level unless perhaps the RGB offsets have been adjusted away from 0.
IMHVO getting the gamma response right is paramount to seeing a good image: No good having a perfect greyscale and gamut if the gamma means shadows are hidden and brighter parts look washed out. Putting the projector in 2.4 or whatever and leaving the other settings alone is only doing half the job. In fact I'd argue that colour temp could be a little way off and you may not even notice since our eyes will tend to compensate, but poor gamma stands out (or it does to me anyway).
It is possible to move the 21 point greyscale around on the Lumagen so that you could have a 1% setting should you wish, but not sure how this effects the autocal result (perhaps you could just move the 5% on down in the Lumagen and use the JVC's 5% control if necessary).
"Don't believe everything you read on the internet". William Shakespeare 1615