Probability of miscasting with Channeling increases dramatically as the CN increases because your Wizard needs many rounds of channeling before they can cast the spell, which is made more risky when the Wizard does not have Atheyric Attunement. Without AA the Wizard always has a 10% chance of rolling a miscast when Channeling.
With a Channel skill 45% = you have 45% chance to add 1 or more SLs, a 3% to crit chance, 50% chance of wasting the round because your rolled failed, and 10% change to miscast which drops to 6% miscast if you have AA.
Because many spells (like Bolt with CN4) need 4SL, you'll likely be spending at least 2 rounds channeling which in turn increases the chance of miscast a lot. Spending 3 rounds to cast Bolt once, with significant risk of miscast each round shows why Channeling is not great.
At skill 55 = 55% of 1+ SL, 5% crit, 41% wasted round, and 10% or 5% miscast.
At skill 65 = 65% of 1+ SL, 5% crit, 31% wasted round, and 10% or 5% miscast.
At skill 75 = 75% of 1+ SL, 6% crit, 22% wasted round, and 10% or 4% miscast.
This is why many Wizards use Petty spells until they have AA and have increased their Channeling skill to at least 70%. And also why often it is better for a Wizard to just dump all their XP into Language Magic and just spam cast the spells, because Channeling has more inherent miscast risk than Casting.
To calculate the actual likelihood of casting a particular spell CN, you'll need a spreadsheet with inputs for your Channel skill, CN target, and AA level --- which is how I got to the rough numbers above.