Not sure what type of screens or solos others are using, but screen in mine doesn't seem to help airflow at all. If anything it seems to slow it down after a few loads as the screen gets a little dirty. Almost always use the screen so bits don't come through the glass one, making a mess of the stem and letting flakes hit my tongue, and probably go all the way down into my lungs. Not really a fan of that.
And sorry, but can't resist saying it any longer..... If you really think the solo is in the same league as the nano, you've either got one hell of a solo you lucked into - or you're not using your nano as well as you could be. I've used solos off and on for a couple years, and just recently bought one of my own. After playing with it for a few weeks, I think I've pretty much seen everything the solo can do. For simple to use portability, it's tough to beat. But next to a nano? It's not even really worth comparing! Not even sure if you could. If I'm in a heavy or quick session by myself the solo heat can't even keep up with my tired old lungs. If you can draw nano heat down like that, I salute you and your fire-breathing lungs! Going to avoid getting too much into the rest of the reasons I feel confident in this assessment, but have to at least mention two - flavor & effeciency.
Back to the nano.... (where we should probably be in this thread anyway!) I seldom have trouble with heat concentrating in the center (green on sides) - but I am a stirrer. Always have been with vapes and think it is necessary to get the most out of your meds with almost every vape. Sometimes there are other ways to "mix" besides stirring (air stir in EQ and to some extent Volcano, shaking MFLB), but it usually pays to mix the load and give it another hit or two before dumping. For the nano it depends on how I'm using it. If "2 hitting" I give a stir after first and second hit (after that it's done, if it makes it that far). If loading a little more & bumping up heat, I take a few hits, stir, repeat until spent.
Temps on the nano (and pretty much everything else) tend to be very subjective - even way beyond how you or I or someone else likes their vapor. There are SO MANY variables. Your stash and how covered with trichs it is; how dry it is; room temp; how close your load is to the heat; size of the load; variations in A/C power where you have it plugged in; variations in the dial itself; wet or dry; how hard you draw; and more!
For me, with my nano, my stems/bubblers, my stash, etc, I can have my heat anywhere from 5.5 to 7.5 depending on what I'm looking for and how I'm playing with the nano that day. Usually for everyday regular use I'm at about 6.25 - 6.5 and going through water. But my nano has the attached cord and is probably a good bit older than most (think it was 10th - 12th one produced), and think it runs a tad hotter (1/4 dial setting? maybe 1/2?) than newer ones. It is going to vary at least some for everyone. Analog dials such as this will seldom be the same from unit to unit and tweaks in production have probably added a bit more variation.
You should also consider the nano's ability to deliver different flavors and effects at different temps & screen levels. Most vapes do this, but the nano excels with it IMO. For instance, I always taste test a new stash at 5.5 with a dry stem and screen pretty close. Flavor is awesome down here, and effect is more heady and less couch lock. IME this type of buzz gives a better comparison of one strain compared to another, and the taste difference part speaks for itself. When you're vaping mostly terpines and a little THC the flavor comes right through and is different for different strains - often even a bit different for different buds from the same plant. Dry is the way to go here, as even a little bit of diffusion will knock down the flavor.
7.5 creates much heavier vapor and will dope you up to get ready to sleep or just be silly stoned. But, if you're throwing that kind of heat on things you're better off moving your screen further away from the heater. Haven't really tried it higher temp with very close screen but can see how this might cause more uneven roasting with hot spot in center and greener around sides. If you're up around these temps, you're probably going to want to use a bubbler. Flavor isn't as pronounced, so diffusion isn't taking much away and a little moisture will go a long way in keeping your throat more comfortable while allowing you to take bigger hits.
For as simple of a device as it is, the nano gives a lot of flexibility - much more than the solo where your option is to do all the same and just adjust the heating number. This is one of the reasons I love the nano more than any other vape I've tried. Whatever you're looking for out of it - or however you use it, you owe it to yourself to play with things a little to see what else it can do. Tweak it a little in both directions and find those subtle differences. Whether you want it to perform differently to cater to your mood or stash - like me and a few others around here; or whether you just want to find your own optimal set-up to go with all the time; a bit of tweaking can make this an incredible vape instead of just merely a good one.
There is much more info in this
post I made a while back, but check it out for a quick tutorial on tweaking and getting your screen where you want it. PLEASE let me know if any of it isn't clear or if you have any questions. THANKS!