Any advice welcome

It is a little lush, but a snapshot in time does not tell the full story as far as how to react. How fast did it get overly lush/dark? The more slowly it got dark, the smaller the adjustmenet necessary. the faster it occured, the bigger the adjustment. Looking over your fertilization over last couple months can help make a better choice of resction, too. Whether you drop it 5-10% or 20% or more immediately depends on context of how it progressed. Be conservative, in either case. Small incremental changes and wait to see how that impacts the darkness of leaves before further adjustments is best... slow progression allows the safest reaction. Painting the walls the brigthest white you can find (RGB hex on label closest to "FF:FF:FF", with a matte finish, not glossy) is a good idea. Get another 10-20% more photons hitting theplants andn from different angles, which should help lower shielded areas more than the canopy, which is a great use of those otherwise wasted photons missing the plant. Don't use shiny, mirror-like material for walls. Even mylar can be a bad idea if it's the smooth surface type. mirror-like reflection is bad. you want diffused light. poly film, orca film, embossed mylar are all equivalent options even if some have a slightly lower absorption rate. The differences are so small that you should go with whatever is most convenient for you. If i didn't use a tent, i'd use white paint.