That's in the normal range for attenuation, what was your mash temperature? Fermentability depends on that. Maize will not give you more fermentable sugars than the rest of the grain, the sugar profile from the maize will be identical to that from the malt at whatever mash temperature. It's just starch being converted by the same enzymes. To add additional fully fermentable sugars while mashing at a higher temperature to get dextrines, you would add simple sugars like dextrose, or cane sugar, to the kettle. Anyway, glad it's mellowing out. RDWHAHB works again!