The CycKit Aeroclam is high, tight, tapered and made of smooth, rounded-edge plastic, so even if you were to get contact, it’s low friction. I don’t think that would happen, but it is wider at the back, so perhaps if you ride off the back of the saddle… Anyway, I love mine— I use two— and the looks are singular.
Cyckit Aeroclam on Fizik Aliante R3
Similar to the Lezyne Microcaddy, Silca’s Mattone is a narrow, rectangular shape that cinches up to the rails with a Boa strap and is roomier than the Aeroclam; I use it for the big 35c tubes on my gravel bike. It parks well inboard of the saddle edges, offering excellent thigh clearance.
Silca Mattone on Fizik Argo Tempo
If you need even more space, the commonly available Specialized Wedge in size L features a tapered shape that’s narrower at the front, though the capacity pushes the nose of the bag further towards the seat post than the other two bags, reducing comparable thigh clearance. I don’t have a problem with it, and the bag is available in S and M sizes as well, so you can get just the right size for your needs. I hold a 47c tube in the L, which is a honking huge piece of rubber.
Specialized Wedge (L) on SQ Lab 611 Active