ned - ah, that's interesting -- let me take a photo or two and see if I can post them up for reference.
The impact is minimal - but where the head tube straps on the Marin were tightened and snug, on the Peregrine (despite the top tube being similar) they were stretched to be even close in fit. But the two sided layout is great, little pockets great, use it on short day rides to carry stuff within triangle rather than on back. can accommodate pack-a-jack, tube, pump, tools..
The Tangle is (I think) a medium, would need to check dimension. The Peregrine is a medium (newer one, 54cm top tube) I'm sure. So, newer medium if that makes sense.
I see your email in profile so may just email it in situ if that's OK fella?