I take it that the reducer/flattener is taking up a fair bit of your available back focus. From the images I have seen, the drawtube only has 50mm of travel (or is it more). That begs the question how far back is the “normal” point of focus?
Perhaps some pics of your setup would help. Is this the product you have?
https://www.astronomyalive.com.au/pr...cer-flattener/