I'll test this out later on my BGT install.
Just to make sure I understand the behavior correctly. SRR non-detection states:
"the wizard makes the recipient undetectable by spells such as Detect Invisibility, Invisibility Purge, and True Seeing"
and
"specific creatures affected with Detect Invisibility or True Seeing will still be able to target the recipient with spellcasting through their improved invisibility for as long as those spells are active, assuming the recipient has already revealed themselves"
Also, after a quick check, Lavok, unlike other liches, doesn't seem to have "Invisibility detection (193)". This might be different on your install. On mine it's not on either of his .cre's nor on any item he carries. BTW I've also noticed spellcasters trying to melee.
Assuming we're just facing a regular spellcaster without this opcode the expected behavior should be:
Any wizard with detect invis/true seeing would not be able to detect you until you commit a hostile action. At that point they would be able to target you with anti-magic spells only as per SCS rules. Creatures with op (193) would presumably not need detect invis/true seeing, but the latter targeting rule (only anti-magic) should still apply? Or maybe (193) allows targeting with any spell, I can't remember.
Bart, this probably doesn't need to be said, but I noticed in your misc. files SR settings.ini you had "anti_magic_spells_pierce = 0". I assume SCS corrects this behavior, but maybe not since it states in the readme v34 under Non-Spell Revisions changes:
"Antimagic attacks penetrate improved invisibility" and "These changes are made only if you are not playing with Spell Revisions."
I set this to 1 in my own game just to be safe.