I looked up your bike, it looks like it has a rack mount attachment on the bottom but not on the top, does that sound right?
Macho Man Disc | All-City Cycles



I recently put a rack on a bike with a similar bike (a full carbon specialized sirrus), and solved it far better than using the brake bridge or p-clamps - they make seatpost collars with a mount point on the seatpost collar.

For seatpost it says "FSA SL280, 27.2mm", but that's the size of the seatpost not the collar. The full carbon Specialized Carbon bike I put the seatpost on is here:
https://www.specialized.com/us/en/bi...-carbon/118220

It also lists the seatpost as "27.2mm", but it also lists the seatpost collar as "rack mount seat collar 31.6mm".

So I believe that this Axiom Trekk Seatpost Collar 31.8mm with rack mounts is the size and kind that would work (and is the one I used that the bike shop sold me):
https://www.amazon.com/Axiom-Trekk-C...3I6/ref=sr_1_1

Yeah it's 31.8mm rather than 31.6, but for a seatpost collar it didn't seem to matter. I also just used a regular Topeak rack like some of the people said above and it worked well. My concern was actually mainly in the rack not being to high and looking silly, though the Sirrus I put it on only has 30mm tires (there was still plenty of clearance for taller tires though).

If you know for sure that you're going to have issues with heelstrike, the racks I know of that sit back further are:
1. Axiom Streamliner Disc (110lb load capacity) (Disc version has a wider top so I prefer it as I use a trunk bag)
2. Axiom Journey Uni-Fit Mk3 Alu (110lb load capacity)
3. Bontrager Backrack Lightweight - a super lightweight rack, probably not what you're looking for but thought I would mention it just in case
4. Old Man Mountain makes some
5. Tubus makes adapters for all their racks that would let you move the rack back the same amount