Keep at it. You'll get it. You might be better served though, just learning for one. Instead of jumping around trying to build for multiple devices, maybe just stick with one of them. Once you get that down, then move into other ones. As you know, each one is a little different, but the principals are the same.
For example, I can build the same coil for an APO, Kayfun, and a Kanger head. All of them can be built identical, however, all have different reading do to placement, configuration, and leg length. The kanger heads are always higher because the leg length is the longest. The Kayfun is then a bit lower because the legs are a touch shorter. Then with the APO it's again just a touch off due to leg length depending on how I place it, or can be halved by utilizing dual coils.
Even though I built all identical coils, same wraps, same ID, same awg wire, variance will happen across devices. Because of these subtle variances, it can become frustrating getting things to work how you want.