You might want to use a Yagi calculator such as the one below to give you some ideas. Normally each director (also known as parasitic) element of a Yagi antenna will decrease in length the further it is from the driven element. They will also get further apart as the distance from the driven element increases. If you are looking for an antenna specifically for RF 8, try modeling a 17 element yagi at 183 MHz using the calculator and compare the results to what you have.
https://www.changpuak.ch/electronics...enna_DL6WU.php