The correct cables I mentioned were for another project but was to share the length one goes to reduce the variables in an antenna system. I actually purchased the cables and antennas on Amazon. To get you familiar with the style and lengths here's some of what I purchased:
https://www.amazon.com/gp/product/B00A4I3AGE/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B019FUHAU8/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1
I used the shorter 3dB antennas (so they don't interfere with the camera) along with the shorter cables from the other kit, on the H, and then then higher gain antennas can be used on the ST16. You can use the longer cables inside the ST16 ---- But, I actually bought a couple sets of both (and some spare cables) since I have two H Advances and I mixed and matched cables. I really think you should poke around and search Amazon to find out what works best for you based on the descriptions of what I bought . I did learn, after purchase, that the thicker coax cable was too hard to easily route inside the H and in certain parts of the ST16 -- So, other cables I ordered where never used. And 20cm length seemed to work well for both H and ST16.
In the end... I have options with antennas and like you, have already invested in the "higher end" 3rd party antennas. If Itelite comes out with their Pro antenna then you certainly can use that alone. Right now, I have my Itelite on one ST16, with two of the higher gain antennas from Amazon for the newer antenna connections I made (that ST16 has 4 connections) and on my other ST16, I use my FPVLR along with another FPVLR antenna for the 2.4GHz connection (that ST16 has only 3 antenna ports) I also could put the higher gain antennas (from Amazon) on the H and just not pan around where the antennas would get in the shot.....But, I have lots of combinations and have not really gone the distance yet to tell you which ones work best. My goal is to have a solid connection within LOS in a relatively high RF environment. The FPVLR antennas allow to be easily placed along with the Itelite panel antenna or all by themselves --- But, I'm not sure you, specifically, plan to purchase the FPVLR antennas soon.