Hey Pierre,
I think you are talking about our second tension bars - and those are an option, but a pretty pricey one. I'm pretty sure that David said that the 160's and 300's could increase a touch, but honestly, after 8 months, I'm just not sure how much stretch is left in the mesh. The retensioning bars would probably just pull the mesh a bit tighter and cause it to pop at this point.
That said, I'd be happy to send a set down to John if he wants to try them out. They should easily bring the mesh up 2-4N. Just let me know if you want to try a set and I will get them headed your way!