Hi Alwayson:
Great Question!
I have the same tight muscles, and can't sit comfortably in Full Lotus either. Hell, I often find discomfort in Half Lotus.
Two things come to mind.
1.Nowhere in the AYP writings does it recommend we should sit in Full Lotus or Half Lotus, only that we sit comfortably.( for me this is a big over-stuffed chair)
2. I think the more we sit comfortably via a daily routine of Deep Meditation the more likely we will be able to sit in Any Lotus position sans discomfort.
Guy