I hate to say this but I have found the fitter I get the higher I go
A week off with any form of injury or cold knocks a good foot off my jumps and takes a couple of weeks to regain
After you get your technique right it then becomes a case of returns for what you put in
I think it boils down to "if you can jump a foot up on your own feet you have evough power to double it on bocks"
I have seen so many people who started bocking after me advance far faster and then when I ask them how they normaly have in the past done something like trampoline, free running or some form of gymnastics
So get fit and spend every available moment on bocks (I manage 1 hour a day week time and at least 4 to 5 on the weekend)
The height will come (and scary it is when it does
)
Jason