I don't think it's that dramatic, just that it can definitely make an
impact over time-- especially with a high light loving plant, which your
Tonina apparently is. I would only consider it one of the variables in
your tank, to be balanced out with everything else (water quality, ferts,
supplements, age and type of substrate, what plants you're growing, your
stocking levels, etc).
I have a lower lighting level than you, and my glosso has always grown
completely flat unless I put it in one of my terrarium setups or had the
lights over the tank off for too long. You might just try poking it back
under your substrate so it's forced to crawl a little more? Also, I've
found that a little substrate fertilizing really helped my glosso. It
might help encourage it to root strongly if it was finding more nutrients
in the substrate than the water column?
Cliff