Well Johndrum...I'll bounce some idea off ya to see what you think.
So you're focusing on the soil aeration issue. It's important. So do the hydroton thing (or perlite, doesn't matter). There's a guy who called himself BOG (Bushy old grower) He sells seeds now but many years ago wrote a book about his grow style. When transplanted up, he left the old soil/rootmass perhaps 1 1/2" above the new soil. Each time he transplanted, he did that so by the time he was in the final 5 gallon pots, the top looked a bit like a wedding cake. He claimed it aided in aeration as well as giving a little more room for roots. You could try that.
I'm currently participating on another thread about whether it's a good idea to aerate water. This is what I will recommend to you...buy a small aquarium pump and airstone and for maybe 10 minutes before watering (or adding nutrient mix) throw the airstone in and let it bubble. That will add some oxygen.
A good wet/dry cycle is important to aeration since as the soil dries, it draws air down into the soil. So make sure you don't overwater...
One final issue...this could be totally unrelated to aeration and roots. When you go into flower and the plant stretches, it's not a bad idea to continue using your N heavy GROW nutrients for the first 2 or 3 weeks...before switching to Bloom nutes. And are you adding a bloom booster at week 5? That's commonly when people do that.
That's all that comes to mind about your situation. Why don't you start a grow thread for your next run to allow the forum to follow along and help.
Peace,
JD