Lyra Helikon setup sensitivity?

I completely agree with Larryi. My Helikon is very sensitive to VTA and I run it with the arm parallel to the record surface using a 180 gram pressing. Also, I feel that it is sensitive to VTF and I run it at the top end of the range at 1.75 grams, no more, no less; after trying it below this in 0.25 gram increments, at least in my rig, this the best VTF.

To set up properly mine on Michell Gyro SE/RB300 I had to use washers between the top cartridge body and headshell to increase the height. VTA has the most of influence to sound in most of Lyras. Quite an effort to set up, but sounds and tracks the best of all.

If you properly use any number of decent protractors, you should be able to attain proper alignment. When you say "multiple geometries," are you really talking about different null points (Baerwald, Lofgren, Stevenson)?

I use to have a Helikon (I now have a Titan). Lyra cartridges have a very narrow specified tracking force range. It is best to stay within that range. Not only does this prevent any damage, but, the cartridge's suspension is set up to ideally work with that particular loading and the coil and former will be in proper alignment with the fixed magnets with that loading. There are those that advocate higher tracking forces than the manufacturer's specifications; I personally would not stray outside of the recommended range even if the sound were better.

I found that both the Helikon and the Titan are a bit sensitive when it comes to VTA--even small changes are audible. But, that appears to be the case with most cartridges that use narrow profile "line contact" stylus types (e.g., Shibata, Ogura, Ortofon Replicant).

The Helikon is just as normal as a lot of other cartridges in set up sensitivity.
Is your Diamond really clean? When there is dirt and dust on it, you will never hear more than subtle differences, no matter what you do.