I've posted this many times.
Take your bib and makes color copies, then apply some sort of fiber [box] tape or duck tape across the back of the copy. Pin the original bib to your singlet / shirt as usual. Now take the color copy and pin it to your outer layer shirt / jacket. Problem solved.
This is the system I used before the advent of timing chips and with the introduction of the Champion Chip in the mid-90's. This mathod worked equally well with the timing strips you attached to your shoes. Now most timing strips come attached to your bib. I've used this method a couple of times with the bib strips w/o fail. With heavy layering I could see the potential for signal interuption.
Youth Has No Age. ~ Picasso / 1st road race: Charleston Distance Run 15 Miler - 1974 / profile
I guess I would just lift my shirt up also as I cross mats. I just wouldn't assume you will be pitching your outer layer. I ran one prior to chips with the intention of pitching an ugly rugby shirt early. I ended up wearing it all 26.2. I lifted it up for pictures and they matched them all somehow.
They are saying the temp will be in the mid-40s and cloudy at the start, which really isn't that cold. But, it's been a warm fall so I'm not as acclimated to the cold as I would like to be yet, and I'm a bit of a slow starter. So I thought I would be more comfortable in an extra light layer for the first 2-3 miles, or if the forecast is wrong.
The photocopy is pretty slick, but I'm not going to have access to one between bib pick-up and race. I think I'll pin my bib somewhat low on my tank top and plan on the lifting my layer (if I end up needing it at all) going over the starting mat.
Life is good.
I wear my race bib on my bottom layer many times. I pin in on my tshirt, then had a jacket, then add a vest (yes, I like to be warm) and I've never had a problem with the chip reading.
No, my race number isn't visible but if someone asks, i can just lift my outer layers and show them.
Of course, that doesn't work for big races if you want photos!
No FedX / Kinkos close by?