On one of markers I have has UMP shroud mounted. The plastics rails have allowed me to insert a wedge shim under the top rail increasing the down angle of the red dot....about 3 degrees or so.

I them determined my average kill zone (say 75ft) zeroed to that distance.

I cursed those plastic rails at first!!! But being able to bend easily to place the shim there has made my red dot a godsend...

On a side note.....

I've started the SIR mod to my other A5 so now I am trying to figure out how create some kind shim or adjustable riser!!!!

I was thinking about using a thick piece of weaver rail to mount my red dot to. Then drill a hole at the rails end to create a pivot and mount to a weaver sling mount or something which would attach to the shroud. On the other end of the rail drill a hole to mount a threaded stud and a adjusting nut to another weaver sling mount. It would be like an adjustable bridge.

But I like what you are putting together!!!!!