This forum is run by the BATC (British Amateur Television Club), it is service made freely available to all interested parties, please do not abuse this privilege.
The Mini-Kits PCB is made from a fairly thin (FR4?) board which has to be mounted flat on the heatsink tight up against the module. There is about 1.5mm or 2mm hight difference between the module lead-in and lead-out out and the PCB so there is about 2mm of lead from the module to the 50 ohm strip line on the board. Could this cause loss at 23cm? If so I will have to make an aluminium spacer between the PCB and the heatsink to raise it.
The datasheet gives a minimum power gain of 23dB with +10dBm in, i.e. 10mW in for 2W out with VDD=12.5V, VGG=5V, so you should check it with those parameters to see if your amp is OK.
It's also very frequency dependent. The datasheet shows typical power gains of around 25dB for +10dBm in at 1240MHz, rising to 31dB at 1240MHz. At 1300MHz it tails off again and is about 5dB down on 1270MHz.
Obviously the gain also drops off with increasing drive power / output power, particularly as you get past P1dB which is around 10W out. You need to take into account cable losses to / from the amp; a couple of feet of 5mm coax will easliy lose a dB or two.