Just inserted the Greater Quen Glyph that was supposed to give 10% boost, but when checking in stats, it only added like 20 damage reduced.

How come and Is it worth it then?

Axii greater glyph added only 0.5sec, instead of 1.1sec that it should have.

But I think that I am starting to understand that it adds to some base and not to the current figure.. Right?

Bump!

Haven't checked on the technical front but what I can say from 139hrs experience, is that many of the runestones & glyphs give such small amounts of bonus as to be laughable! I go by my actual experience in the game. I save, fit a perk, then tackle a monster. I can say that many, if not most of the perks have no significant effect really. Mostly I think it's a very gradual accretion of bonuses that slowly improves your abilities. Also it's hard to tell anyway, as my inventory & crafting UI continually lists such items wrongly! :)

The percentage increases you get for runes, glyphs, potions, etc are applied to a base amount, not the total shown in player stats; e.g. if you have 6 Greater Quens installed on pieces of your armor the increase will be 60% of the base amount not the 77% you would get by raising 1.1 to the 6th power.

Take your point JAA but when you apply such buffs, do you notice a significant difference in the way your Quenn protects you? Anyway, as I said, the damned bugs in this game make a lot of these arguments spurious. Classic example, I've invested several points in Yrden ability, yet consistently when I fight Wraiths, the damned thing just won't work! What's a wind up about it, is that Geralt does the motion, there's a phttt noise, but no Yrden signs on the ground! Still, we gotta do something other than just kill Monsters I suppose. :)

I went with a sign based build and towards the end game I had 33 skill points in spells, I wore some version of griffin armor (sign intensity enhanced by veles) through out from about level 8, and was addicted to tawny owl and Peteris philter. Using Quen, I noticed that as I went up in level getting shot by bad guys using crossbows went from damaging me to no noticeable damage but staggered to just slowed down as I moved in for the kill (how much was quen and how much armor and increased level I do not know).
I did kill a noonwraith (guarding the pirate treasure on an island) using the yrden sign (the alternate sign that shoots lightening).

Some times sign boosting is more obvious than others. I have 'exploding quenn' & at one point I'm escorting Triss thru the sewers when she's set upon by a whole pack of rats. I had some stairs to get down, but as her health bar had begun to diminish with the rats swarming on her, I jumped straight down to her position, with my sword drawn for action. There was a crackling of a dozen or more rapid pops & the whole swarm was taken out by my exploding quenn shield! Lol. Triss, having been screaming in jeopardy, merely carried on conversing with me. Not a jot of thanks! It's no wonder I chose Yen over her. :)