dumb question about tire size?

I've ordered a set of snow tires from the tirerack folks for a 2007 base cayman. The tires are on their way to me. However, I just noticed that the size of the rears that are being shipped doesn't match the owner's manual or even tirerack's own online suggested size for my car. I ended up placing the order over the phone (long story) and I wonder if there was some miscommunication between me and the operator resulting in this difference. The recommended rears (again, owner's manual and tirerack website) are 235/50/R17, while the tires that are on their way to me are 235/45/R17. If I understand those numbers, it means that the sidewall height on the ones I'm receiving is 45% of 235 mm, instead of 55% of 235 mm, making for I guess an overall height (floor to top of tire) which is about 24 mm smaller than recommended. Will this make for any problems?

Incidentally, I would love it if they will fit on both the 2007 cayman and a 2003 base boxster. Does anyone know if this little mixup works in my favor for that?

I called the tire rack folks to ask what they thought. They thanked me for catching it and said it shouldn't have gone through. They asked that I refuse the original order when it arrives, and they shipped out a corrected order and charged me only the difference. Impressive service.