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No, it seems you are mistaken. )
The difference is more than 10%. You don't seem to be taking specialization into account, and that's what this whole discussion is about.
It receives an additional 5% per level to the percentage value of the Wizardry skill. The number of raised units (%) is calculated using the formula:
k*(1+0.05*Level),
where k = 10 for the basic level of the secondary skill Wizardry
k = 20 for the advanced level
k = 30 for the expert level
The maximum significant level for this skill is 100%
Isra and Vidomina are most dangerous when freed from prison (if they are unbanned) at level 5...
Added 2 minutes ago
Now, read your post carefully again. You are all in some kind of somnambulistic state. You read, but you completely don't understand what you read. Is Vidomina with advanced necromancy no longer a necromancy specialist? :D What is the difference between k=20 and k=30?