First a saying "The higher the better" (within reason) it's a calculus job to figure out what the crossover point is but the higher the antenna (outside)
1: The farther it is from the inside antenna
2: The stronger the signal it can receive (or the farther it can see take your pick)
3: The greater the line loss if the amplifier is in the house (You can put the amplifier in a weatherproof box closer to the outside antenna and go quite high)
Next. there are direcitonal antennas. One is described in another post in this same forum.. Those greatly extend your range. each 3 DB gain = 1.4x distance. OR MORE.