If you place you mvb bulb 16 inches up you would
Want something high wattage, such as a zoo med 100w powersun uvb and heat
Or exo terra makes a higher wattage 120w and
160w thats mvb and heat, that would be your
I use the exo terra 120w its great!
For a 100 Watt MVB, I have read to have it between 12 and 18 inches from the tort for it to be safe (whatever distance to get your desired basking temp) but different brands may have different requirements, so its best to read the packaging. Similarly, a 160 Watt MVB typically is 16 to 24 inches. Yes, closer gets the tort more UVB, but too close is too hot so they will bask outside the sweet spot radius, so best to get their ideal basking temp. They will bask plenty to get the UVB they need anyways. ie. I would not place the bulb at the minimum assuming its best. You need to place it to get the correct temp, within the safe range. They can take a few hours to warm up, so don't measure temps right after you turn it on.
I'd typically recommend T-Rex Active UV Heat or Mega Ray, but they both seem to be having some availability issues now, so I'd go with a ZooMed Powersun. There isn't any current data on UVB output of MVBs however. I have not heard as much good feedback anecdotally on in the past about any other brands but Mega Ray, T-Rex, and Powersun. You want a vertically adjustable lamp stand so you can adjust it as needed (never just have one distance available to place your bulb). As the room temp changes, you will need to make slight adjustments. An accurate thermometer like a temp gun is crutial.
Wow what basking temp do you get at 12 inches? I have it at about 14/15 inches in our 60F high humidity house to get 95 F basking temp at the substrate (hotter for the tort). My tort still tends to bask to the side of the sweet spot with that temp.
With the room being around 75-80F the basking temps are around 95F for me as well... the humidity here is naturally around 60-90% good for the tort I guess ! The thing with them is also they do thermo regulate... as long as there is a cool spot they'll just roam around and get comfortable.