I've also been interested in the sizing of the current long-sleeved polos and long-sleeved Mickey-head t-shirts at DisneyShopping.com. I assume this is what you're talking about, right?
I don't have the answer, but we also have the most recent short-sleeved shirts (which I would have said had antenna balls on them, instead of fishing bobbers - so perhaps that might help clarify it for someone else).
Are you asking about child or adult sizes? I think that would make a difference. I found that the children's short-sleeved antenna ball t-shirts ran extremely large, and I had to order a size down from what I typically order. Conversely, I ordered the boys's short-sleeved polos and found that they ran extremely, ridiculously small. For example, my 7 year old average size son needed a small in the t-shirt, yet the large in the polo is just barely big enough (he could have used an XL if they had it).
Because of this crazy recent kids' sizing, I've been afraid to try either the long-sleeved polo or Mickey head t-shirt. I'd love to see any real-life experiences with sizing though.
For what it's worth, I thought the sizing on the adult short-sleeve polo and antenna ball t-shirts was true-to-size (for both men & women).