Daytrana question, quick info needed! | ADHD Information

Ds takes 40 mg ritalin la, and has been on this dose for a year and a half.  He probably weighs 100 lbs.  The scrip the pdoc gave me was for 30mg.  Does that sound right?  I'm looking for a ball-park guide.  I know that the dosage is supposed to be lower on the patch, and I thought it was supposed to be about half.  Should I call the Doc and ask for a lower dose?
Well for my son who is 5 and was on 20 focalin xr in the am and 10 in the pm, the 20 mg patch suited him just fine all day.  The patch is wonderful!!  Last all day!!!  But I think he is having a reaction to the patch being on his skin that we may not be able to contine.  So id say 30 is a good start. you never know, the patch gives a constance flow of meds (no upper and downer affects) it might be just right for him.  It was advised we start out lower (which was 15 mg) but it did not faze him.  Does the patch go to 40 mg?