Follicle Size day of the trigger shot

What size follicles are ideal for triggering? My doctor said I had an 18mm on my right ovary and the one in my left side was bigger than he would like to see it. But he likes to trigger with follicles 15-20mms and no more than 20mms so I am thinking my follicle on the left was probably in the 20's. Is that still good for the trigger? My right side tube is partially blocked and that is the side with the 18mms follicle. My doctor said my left fallopian tube could possiblypick it up...what does he mean by that?