fortunately you are inncorrect. You can put Bombard on Spell Trigger if you reach 120 mystic with 120 focus (real or altered).
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I do not know the formula to calculate the spell casting success, I don't believe it has ever been published, but in order to cast spell trigger 100% I try and hit at least 75 Real skill usually 80 so I am not left with 5 unused points.
Nice find here OP.
edit: for clarification I reach 80 real skill then get the extra 40 points on jewels/book to get me to 120 mysticism so I can cast Spell Trigger and get Bombard. Then once I take jewels/book off I am at 80 real skill so I can cast bombard with 100% success. It takes 45 skill to cast and typically it's 30 points above for 100% success.