Amplifiers don't work like that. I am guessing it just isn't pointing in the right direction and being a high powered one, it is actually more sensitive to being accurate than a less sensitive.
Think of it as an angle - unless that angle is directly at the Mast, you won't pick it up.
If you can find the mast on a map then know what degree it is at compared to you, then you should get a decent signal.
If the amplifier is directional then it may need to be rotated as ElectrO_90 suggests. If the antenna is passive then do get one with a signal amplifier. The distance rating isn't often accurate in antennas.