This is a remix of the 6.15in part found in Compliant Rail Covers V1.1 by @QwermMakes.

I made this to give me a higher comb height and more surface area than the included riser/cover that comes with the A3 Tactical Triad bullpup kit and Foxtrot Mike FM-15 upper.  I basically just used the Thicken feature in OnShape for the center section, adding .25 inches.   

This should also work on any other bullpup conversion kit that has a full length 1913 rail on the upper receiver (BRN-180, PSA JAKL, etc.) 
 

Pictured riser was printed in black Polymide PA6-CF on a P1S with hardened steel nozzle.  I recommend PETG, PA, or ABS to handle heat.  TPU and PLA can work, but could have heat or durability issues.

“Triad” text is a separate object that can be deleted or edited.  

EDIT: I've added another profile that extends the cover on the right side, to act as a case deflector for left-handed shooters.

.20 Layer Height

2 Walls

20% Sparse Infill (Increase this if using PLA)

Original author recommends printing on side, but I got best results with PA6-CF printing upright, latch side on bottom, with snug supports and brim.