433 Mhz + Attiny85 improve range
I tried those antennae and I got better range with a whip antenna made from 17cm of copper wire. Probably 1/3 to 1/2 better.
Like you I'm combining an ATTiny85 and 433mhz transmitter. The transmitter definitely works better with 12V though it works quite well on 4.5V with good line of sight over about 40m for me.
When I tried a 7085 in my circuit the 12v battery did not last many hours (about 6? I left it overnight and it was dead in the morning). I did not use an NPN, I just connected the data from the transmitter to one of the ATTiny pins. It worked fine except for the battery drain which I am still trying to solve.